diff options
Diffstat (limited to 'drivers/lguest')
| -rw-r--r-- | drivers/lguest/core.c | 5 | ||||
| -rw-r--r-- | drivers/lguest/hypercalls.c | 11 | ||||
| -rw-r--r-- | drivers/lguest/interrupts_and_traps.c | 37 | ||||
| -rw-r--r-- | drivers/lguest/lg.h | 4 | ||||
| -rw-r--r-- | drivers/lguest/lguest_device.c | 11 | ||||
| -rw-r--r-- | drivers/lguest/lguest_user.c | 23 | ||||
| -rw-r--r-- | drivers/lguest/page_tables.c | 113 | ||||
| -rw-r--r-- | drivers/lguest/segments.c | 48 | ||||
| -rw-r--r-- | drivers/lguest/x86/core.c | 120 | ||||
| -rw-r--r-- | drivers/lguest/x86/switcher_32.S | 71 |
10 files changed, 274 insertions, 169 deletions
diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c index 35d19ae58de..cb4c67025d5 100644 --- a/drivers/lguest/core.c +++ b/drivers/lguest/core.c @@ -128,9 +128,12 @@ static void unmap_switcher(void) __free_pages(switcher_page[i], 0); } -/*L:305 +/*H:032 * Dealing With Guest Memory. * + * Before we go too much further into the Host, we need to grok the routines + * we use to deal with Guest memory. + * * When the Guest gives us (what it thinks is) a physical address, we can use * the normal copy_from_user() & copy_to_user() on the corresponding place in * the memory region allocated by the Launcher. diff --git a/drivers/lguest/hypercalls.c b/drivers/lguest/hypercalls.c index 9d5184c7c14..b478affe8f9 100644 --- a/drivers/lguest/hypercalls.c +++ b/drivers/lguest/hypercalls.c @@ -90,6 +90,7 @@ static void do_hcall(struct lguest *lg, struct hcall_args *args) lg->pending_notify = args->arg1; break; default: + /* It should be an architecture-specific hypercall. */ if (lguest_arch_do_hcall(lg, args)) kill_guest(lg, "Bad hypercall %li\n", args->arg0); } @@ -157,7 +158,6 @@ static void do_async_hcalls(struct lguest *lg) * Guest makes a hypercall, we end up here to set things up: */ static void initialize(struct lguest *lg) { - /* You can't do anything until you're initialized. The Guest knows the * rules, so we're unforgiving here. */ if (lg->hcall->arg0 != LHCALL_LGUEST_INIT) { @@ -174,7 +174,8 @@ static void initialize(struct lguest *lg) || get_user(lg->noirq_end, &lg->lguest_data->noirq_end)) kill_guest(lg, "bad guest page %p", lg->lguest_data); - /* We write the current time into the Guest's data page once now. */ + /* We write the current time into the Guest's data page once so it can + * set its clock. */ write_timestamp(lg); /* page_tables.c will also do some setup. */ @@ -182,8 +183,8 @@ static void initialize(struct lguest *lg) /* This is the one case where the above accesses might have been the * first write to a Guest page. This may have caused a copy-on-write - * fault, but the Guest might be referring to the old (read-only) - * page. */ + * fault, but the old page might be (read-only) in the Guest + * pagetable. */ guest_pagetable_clear_all(lg); } @@ -220,7 +221,7 @@ void do_hypercalls(struct lguest *lg) * Normally it doesn't matter: the Guest will run again and * update the trap number before we come back here. * - * However, if we are signalled or the Guest sends DMA to the + * However, if we are signalled or the Guest sends I/O to the * Launcher, the run_guest() loop will exit without running the * Guest. When it comes back it would try to re-run the * hypercall. */ diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c index 82966982cb3..2b66f79c208 100644 --- a/drivers/lguest/interrupts_and_traps.c +++ b/drivers/lguest/interrupts_and_traps.c @@ -92,8 +92,8 @@ static void set_guest_interrupt(struct lguest *lg, u32 lo, u32 hi, int has_err) /* Remember that we never let the Guest actually disable interrupts, so * the "Interrupt Flag" bit is always set. We copy that bit from the - * Guest's "irq_enabled" field into the eflags word: the Guest copies - * it back in "lguest_iret". */ + * Guest's "irq_enabled" field into the eflags word: we saw the Guest + * copy it back in "lguest_iret". */ eflags = lg->regs->eflags; if (get_user(irq_enable, &lg->lguest_data->irq_enabled) == 0 && !(irq_enable & X86_EFLAGS_IF)) @@ -124,7 +124,7 @@ static void set_guest_interrupt(struct lguest *lg, u32 lo, u32 hi, int has_err) kill_guest(lg, "Disabling interrupts"); } -/*H:200 +/*H:205 * Virtual Interrupts. * * maybe_do_interrupt() gets called before every entry to the Guest, to see if @@ -256,19 +256,21 @@ int deliver_trap(struct lguest *lg, unsigned int num) * bogus one in): if we fail here, the Guest will be killed. */ if (!idt_present(lg->arch.idt[num].a, lg->arch.idt[num].b)) return 0; - set_guest_interrupt(lg, lg->arch.idt[num].a, lg->arch.idt[num].b, has_err(num)); + set_guest_interrupt(lg, lg->arch.idt[num].a, lg->arch.idt[num].b, + has_err(num)); return 1; } /*H:250 Here's the hard part: returning to the Host every time a trap happens * and then calling deliver_trap() and re-entering the Guest is slow. - * Particularly because Guest userspace system calls are traps (trap 128). + * Particularly because Guest userspace system calls are traps (usually trap + * 128). * * So we'd like to set up the IDT to tell the CPU to deliver traps directly * into the Guest. This is possible, but the complexities cause the size of * this file to double! However, 150 lines of code is worth writing for taking * system calls down from 1750ns to 270ns. Plus, if lguest didn't do it, all - * the other hypervisors would tease it. + * the other hypervisors would beat it up at lunchtime. * * This routine indicates if a particular trap number could be delivered * directly. */ @@ -331,7 +333,7 @@ void pin_stack_pages(struct lguest *lg) * change stacks on each context switch. */ void guest_set_stack(struct lguest *lg, u32 seg, u32 esp, unsigned int pages) { - /* You are not allowd have a stack segment with privilege level 0: bad + /* You are not allowed have a stack segment with privilege level 0: bad * Guest! */ if ((seg & 0x3) != GUEST_PL) kill_guest(lg, "bad stack segment %i", seg); @@ -350,7 +352,7 @@ void guest_set_stack(struct lguest *lg, u32 seg, u32 esp, unsigned int pages) * part of the Host: page table handling. */ /*H:235 This is the routine which actually checks the Guest's IDT entry and - * transfers it into our entry in "struct lguest": */ + * transfers it into the entry in "struct lguest": */ static void set_trap(struct lguest *lg, struct desc_struct *trap, unsigned int num, u32 lo, u32 hi) { @@ -456,6 +458,18 @@ void copy_traps(const struct lguest *lg, struct desc_struct *idt, } } +/*H:200 + * The Guest Clock. + * + * There are two sources of virtual interrupts. We saw one in lguest_user.c: + * the Launcher sending interrupts for virtual devices. The other is the Guest + * timer interrupt. + * + * The Guest uses the LHCALL_SET_CLOCKEVENT hypercall to tell us how long to + * the next timer interrupt (in nanoseconds). We use the high-resolution timer + * infrastructure to set a callback at that time. + * + * 0 means "turn off the clock". */ void guest_set_clockevent(struct lguest *lg, unsigned long delta) { ktime_t expires; @@ -466,20 +480,27 @@ void guest_set_clockevent(struct lguest *lg, unsigned long delta) return; } + /* We use wallclock time here, so the Guest might not be running for + * all the time between now and the timer interrupt it asked for. This + * is almost always the right thing to do. */ expires = ktime_add_ns(ktime_get_real(), delta); hrtimer_start(&lg->hrt, expires, HRTIMER_MODE_ABS); } +/* This is the function called when the Guest's timer expires. */ static enum hrtimer_restart clockdev_fn(struct hrtimer *timer) { struct lguest *lg = container_of(timer, struct lguest, hrt); + /* Remember the first interrupt is the timer interrupt. */ set_bit(0, lg->irqs_pending); + /* If the Guest is actually stopped, we need to wake it up. */ if (lg->halted) wake_up_process(lg->tsk); return HRTIMER_NORESTART; } +/* This sets up the timer for this Guest. */ void init_clockdev(struct lguest *lg) { hrtimer_init(&lg->hrt, CLOCK_REALTIME, HRTIMER_MODE_ABS); diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h index 0c74ac42cf0..86924891b5e 100644 --- a/drivers/lguest/lg.h +++ b/drivers/lguest/lg.h @@ -100,7 +100,7 @@ int lguest_address_ok(const struct lguest *lg, void __lgread(struct lguest *, void *, unsigned long, unsigned); void __lgwrite(struct lguest *, unsigned long, const void *, unsigned); -/*L:306 Using memory-copy operations like that is usually inconvient, so we +/*H:035 Using memory-copy operations like that is usually inconvient, so we * have the following helper macros which read and write a specific type (often * an unsigned long). * @@ -188,7 +188,7 @@ void write_timestamp(struct lguest *lg); * Let's step aside for the moment, to study one important routine that's used * widely in the Host code. * - * There are many cases where the Guest does something invalid, like pass crap + * There are many cases where the Guest can do something invalid, like pass crap * to a hypercall. Since only the Guest kernel can make hypercalls, it's quite * acceptable to simply terminate the Guest and give the Launcher a nicely * formatted reason. It's also simpler for the Guest itself, which doesn't diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c index 71c64837b43..8904f72f97c 100644 --- a/drivers/lguest/lguest_device.c +++ b/drivers/lguest/lguest_device.c @@ -53,7 +53,8 @@ struct lguest_device { * Device configurations * * The configuration information for a device consists of a series of fields. - * The device will look for these fields during setup. + * We don't really care what they are: the Launcher set them up, and the driver + * will look at them during setup. * * For us these fields come immediately after that device's descriptor in the * lguest_devices page. @@ -122,8 +123,8 @@ static void lg_set_status(struct virtio_device *vdev, u8 status) * The other piece of infrastructure virtio needs is a "virtqueue": a way of * the Guest device registering buffers for the other side to read from or * write into (ie. send and receive buffers). Each device can have multiple - * virtqueues: for example the console has one queue for sending and one for - * receiving. + * virtqueues: for example the console driver uses one queue for sending and + * another for receiving. * * Fortunately for us, a very fast shared-memory-plus-descriptors virtqueue * already exists in virtio_ring.c. We just need to connect it up. @@ -158,7 +159,7 @@ static void lg_notify(struct virtqueue *vq) * * This is kind of an ugly duckling. It'd be nicer to have a standard * representation of a virtqueue in the configuration space, but it seems that - * everyone wants to do it differently. The KVM guys want the Guest to + * everyone wants to do it differently. The KVM coders want the Guest to * allocate its own pages and tell the Host where they are, but for lguest it's * simpler for the Host to simply tell us where the pages are. * @@ -284,6 +285,8 @@ static void add_lguest_device(struct lguest_device_desc *d) { struct lguest_device *ldev; + /* Start with zeroed memory; Linux's device layer seems to count on + * it. */ ldev = kzalloc(sizeof(*ldev), GFP_KERNEL); if (!ldev) { printk(KERN_EMERG "Cannot allocate lguest dev %u\n", diff --git a/drivers/lguest/lguest_user.c b/drivers/lguest/lguest_user.c index ee405b38383..9d716fa42ca 100644 --- a/drivers/lguest/lguest_user.c +++ b/drivers/lguest/lguest_user.c @@ -8,20 +8,22 @@ #include <linux/fs.h> #include "lg.h" -/*L:315 To force the Guest to stop running and return to the Launcher, the - * Waker sets writes LHREQ_BREAK and the value "1" to /dev/lguest. The - * Launcher then writes LHREQ_BREAK and "0" to release the Waker. */ +/*L:055 When something happens, the Waker process needs a way to stop the + * kernel running the Guest and return to the Launcher. So the Waker writes + * LHREQ_BREAK and the value "1" to /dev/lguest to do this. Once the Launcher + * has done whatever needs attention, it writes LHREQ_BREAK and "0" to release + * the Waker. */ static int break_guest_out(struct lguest *lg, const unsigned long __user *input) { unsigned long on; - /* Fetch whether they're turning break on or off.. */ + /* Fetch whether they're turning break on or off. */ if (get_user(on, input) != 0) return -EFAULT; if (on) { lg->break_out = 1; - /* Pop it out (may be running on different CPU) */ + /* Pop it out of the Guest (may be running on different CPU) */ wake_up_process(lg->tsk); /* Wait for them to reset it */ return wait_event_interruptible(lg->break_wq, !lg->break_out); @@ -58,7 +60,7 @@ static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o) if (!lg) return -EINVAL; - /* If you're not the task which owns the guest, go away. */ + /* If you're not the task which owns the Guest, go away. */ if (current != lg->tsk) return -EPERM; @@ -92,8 +94,8 @@ static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o) * base: The start of the Guest-physical memory inside the Launcher memory. * * pfnlimit: The highest (Guest-physical) page number the Guest should be - * allowed to access. The Launcher has to live in Guest memory, so it sets - * this to ensure the Guest can't reach it. + * allowed to access. The Guest memory lives inside the Launcher, so it sets + * this to ensure the Guest can only reach its own memory. * * pgdir: The (Guest-physical) address of the top of the initial Guest * pagetables (which are set up by the Launcher). @@ -189,7 +191,7 @@ unlock: } /*L:010 The first operation the Launcher does must be a write. All writes - * start with a 32 bit number: for the first write this must be + * start with an unsigned long number: for the first write this must be * LHREQ_INITIALIZE to set up the Guest. After that the Launcher can use * writes of other values to send interrupts. */ static ssize_t write(struct file *file, const char __user *in, @@ -275,8 +277,7 @@ static int close(struct inode *inode, struct file *file) * The Launcher is the Host userspace program which sets up, runs and services * the Guest. In fact, many comments in the Drivers which refer to "the Host" * doing things are inaccurate: the Launcher does all the device handling for - * the Guest. The Guest can't tell what's done by the the Launcher and what by - * the Host. + * the Guest, but the Guest can't know that. * * Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we * shall see more of that later. diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c index 2a45f0691c9..fffabb32715 100644 --- a/drivers/lguest/page_tables.c +++ b/drivers/lguest/page_tables.c @@ -26,7 +26,8 @@ * * We use two-level page tables for the Guest. If you're not entirely * comfortable with virtual addresses, physical addresses and page tables then - * I recommend you review lguest.c's "Page Table Handling" (with diagrams!). + * I recommend you review arch/x86/lguest/boot.c's "Page Table Handling" (with + * diagrams!). * * The Guest keeps page tables, but we maintain the actual ones here: these are * called "shadow" page tables. Which is a very Guest-centric name: these are @@ -36,11 +37,11 @@ * * Anyway, this is the most complicated part of the Host code. There are seven * parts to this: - * (i) Setting up a page table entry for the Guest when it faults, - * (ii) Setting up the page table entry for the Guest stack, - * (iii) Setting up a page table entry when the Guest tells us it has changed, + * (i) Looking up a page table entry when the Guest faults, + * (ii) Making sure the Guest stack is mapped, + * (iii) Setting up a page table entry when the Guest tells us one has changed, * (iv) Switching page tables, - * (v) Flushing (thowing away) page tables, + * (v) Flushing (throwing away) page tables, * (vi) Mapping the Switcher when the Guest is about to run, * (vii) Setting up the page tables initially. :*/ @@ -57,16 +58,15 @@ static DEFINE_PER_CPU(pte_t *, switcher_pte_pages); #define switcher_pte_page(cpu) per_cpu(switcher_pte_pages, cpu) -/*H:320 With our shadow and Guest types established, we need to deal with - * them: the page table code is curly enough to need helper functions to keep - * it clear and clean. +/*H:320 The page table code is curly enough to need helper functions to keep it + * clear and clean. * * There are two functions which return pointers to the shadow (aka "real") * page tables. * * spgd_addr() takes the virtual address and returns a pointer to the top-level - * page directory entry for that address. Since we keep track of several page - * tables, the "i" argument tells us which one we're interested in (it's + * page directory entry (PGD) for that address. Since we keep track of several + * page tables, the "i" argument tells us which one we're interested in (it's * usually the current one). */ static pgd_t *spgd_addr(struct lguest *lg, u32 i, unsigned long vaddr) { @@ -81,9 +81,9 @@ static pgd_t *spgd_addr(struct lguest *lg, u32 i, unsigned long vaddr) return &lg->pgdirs[i].pgdir[index]; } -/* This routine then takes the PGD entry given above, which contains the - * address of the PTE page. It then returns a pointer to the PTE entry for the - * given address. */ +/* This routine then takes the page directory entry returned above, which + * contains the address of the page table entry (PTE) page. It then returns a + * pointer to the PTE entry for the given address. */ static pte_t *spte_addr(struct lguest *lg, pgd_t spgd, unsigned long vaddr) { pte_t *page = __va(pgd_pfn(spgd) << PAGE_SHIFT); @@ -191,7 +191,7 @@ static void check_gpgd(struct lguest *lg, pgd_t gpgd) } /*H:330 - * (i) Setting up a page table entry for the Guest when it faults + * (i) Looking up a page table entry when the Guest faults. * * We saw this call in run_guest(): when we see a page fault in the Guest, we * come here. That's because we only set up the shadow page tables lazily as @@ -199,7 +199,7 @@ static void check_gpgd(struct lguest *lg, pgd_t gpgd) * and return to the Guest without it knowing. * * If we fixed up the fault (ie. we mapped the address), this routine returns - * true. */ + * true. Otherwise, it was a real fault and we need to tell the Guest. */ int demand_page(struct lguest *lg, unsigned long vaddr, int errcode) { pgd_t gpgd; @@ -246,16 +246,16 @@ int demand_page(struct lguest *lg, unsigned long vaddr, int errcode) if ((errcode & 2) && !(pte_flags(gpte) & _PAGE_RW)) return 0; - /* User access to a kernel page? (bit 3 == user access) */ + /* User access to a kernel-only page? (bit 3 == user access) */ if ((errcode & 4) && !(pte_flags(gpte) & _PAGE_USER)) return 0; /* Check that the Guest PTE flags are OK, and the page number is below * the pfn_limit (ie. not mapping the Launcher binary). */ check_gpte(lg, gpte); + /* Add the _PAGE_ACCESSED and (for a write) _PAGE_DIRTY flag */ gpte = pte_mkyoung(gpte); - if (errcode & 2) gpte = pte_mkdirty(gpte); @@ -272,23 +272,28 @@ int demand_page(struct lguest *lg, unsigned long vaddr, int errcode) else /* If this is a read, don't set the "writable" bit in the page * table entry, even if the Guest says it's writable. That way - * we come back here when a write does actually ocur, so we can - * update the Guest's _PAGE_DIRTY flag. */ + * we will come back here when a write does actually occur, so + * we can update the Guest's _PAGE_DIRTY flag. */ *spte = gpte_to_spte(lg, pte_wrprotect(gpte), 0); /* Finally, we write the Guest PTE entry back: we've set the * _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags. */ lgwrite(lg, gpte_ptr, pte_t, gpte); - /* We succeeded in mapping the page! */ + /* The fault is fixed, the page table is populated, the mapping + * manipulated, the result returned and the code complete. A small + * delay and a trace of alliteration are the only indications the Guest + * has that a page fault occurred at all. */ return 1; } -/*H:360 (ii) Setting up the page table entry for the Guest stack. +/*H:360 + * (ii) Making sure the Guest stack is mapped. * - * Remember pin_stack_pages() which makes sure the stack is mapped? It could - * simply call demand_page(), but as we've seen that logic is quite long, and - * usually the stack pages are already mapped anyway, so it's not required. + * Remember that direct traps into the Guest need a mapped Guest kernel stack. + * pin_stack_pages() calls us here: we could simply call demand_page(), but as + * we've seen that logic is quite long, and usually the stack pages are already + * mapped, so it's overkill. * * This is a quick version which answers the question: is this virtual address * mapped by the shadow page tables, and is it writable? */ @@ -297,7 +302,7 @@ static int page_writable(struct lguest *lg, unsigned long vaddr) pgd_t *spgd; unsigned long flags; - /* Look at the top level entry: is it present? */ + /* Look at the current top level entry: is it present? */ spgd = spgd_addr(lg, lg->pgdidx, vaddr); if (!(pgd_flags(*spgd) & _PAGE_PRESENT)) return 0; @@ -333,15 +338,14 @@ static void release_pgd(struct lguest *lg, pgd_t *spgd) release_pte(ptepage[i]); /* Now we can free the page of PTEs */ free_page((long)ptepage); - /* And zero out the PGD entry we we never release it twice. */ + /* And zero out the PGD entry so we never release it twice. */ *spgd = __pgd(0); } } -/*H:440 (v) Flushing (thowing away) page tables, - * - * We saw flush_user_mappings() called when we re-used a top-level pgdir page. - * It simply releases every PTE page from 0 up to the kernel address. */ +/*H:445 We saw flush_user_mappings() twice: once from the flush_user_mappings() + * hypercall and once in new_pgdir() when we re-used a top-level pgdir page. + * It simply releases every PTE page from 0 up to the Guest's kernel address. */ static void flush_user_mappings(struct lguest *lg, int idx) { unsigned int i; @@ -350,8 +354,10 @@ static void flush_user_mappings(struct lguest *lg, int idx) release_pgd(lg, lg->pgdirs[idx].pgdir + i); } -/* The Guest also has a hypercall to do this manually: it's used when a large - * number of mappings have been changed. */ +/*H:440 (v) Flushing (throwing away) page tables, + * + * The Guest has a hypercall to throw away the page tables: it's used when a + * large number of mappings have been changed. */ void guest_pagetable_flush_user(struct lguest *lg) { /* Drop the userspace part of the current page table. */ @@ -423,8 +429,9 @@ static unsigned int new_pgdir(struct lguest *lg, /*H:430 (iv) Switching page tables * - * This is what happens when the Guest changes page tables (ie. changes the - * top-level pgdir). This happens on almost every context switch. */ + * Now we've seen all the page table setting and manipulation, let's see what + * what happens when the Guest changes page tables (ie. changes the top-level + * pgdir). This occurs on almost every context switch. */ void guest_new_pagetable(struct lguest *lg, unsigned long pgtable) { int newpgdir, repin = 0; @@ -443,7 +450,8 @@ void guest_new_pagetable(struct lguest *lg, unsigned long pgtable) } /*H:470 Finally, a routine which throws away everything: all PGD entries in all - * the shadow page tables. This is used when we destroy the Guest. */ + * the shadow page tables, including the Guest's kernel mappings. This is used + * when we destroy the Guest. */ static void release_all_pagetables(struct lguest *lg) { unsigned int i, j; @@ -458,13 +466,22 @@ static void release_all_pagetables(struct lguest *lg) /* We also throw away everything when a Guest tells us it's changed a kernel * mapping. Since kernel mappings are in every page table, it's easiest to - * throw them all away. This is amazingly slow, but thankfully rare. */ + * throw them all away. This traps the Guest in amber for a while as + * everything faults back in, but it's rare. */ void guest_pagetable_clear_all(struct lguest *lg) { release_all_pagetables(lg); /* We need the Guest kernel stack mapped again. */ pin_stack_pages(lg); } +/*:*/ +/*M:009 Since we throw away all mappings when a kernel mapping changes, our + * performance sucks for guests using highmem. In fact, a guest with + * PAGE_OFFSET 0xc0000000 (the default) and more than about 700MB of RAM is + * usually slower than a Guest with less memory. + * + * This, of course, cannot be fixed. It would take some kind of... well, I + * don't know, but the term "puissant code-fu" comes to mind. :*/ /*H:420 This is the routine which actually sets the page table entry for then * "idx"'th shadow page table. @@ -483,7 +500,7 @@ void guest_pagetable_clear_all(struct lguest *lg) static void do_set_pte(struct lguest *lg, int idx, unsigned long vaddr, pte_t gpte) { - /* Look up the matching shadow page directot entry. */ + /* Look up the matching shadow page directory entry. */ pgd_t *spgd = spgd_addr(lg, idx, vaddr); /* If the top level isn't present, there's no entry to update. */ @@ -500,7 +517,8 @@ static void do_set_pte(struct lguest *lg, int idx, *spte = gpte_to_spte(lg, gpte, pte_flags(gpte) & _PAGE_DIRTY); } else - /* Otherwise we can demand_page() it in later. */ + /* Otherwise kill it and we can demand_page() it in + * later. */ *spte = __pte(0); } } @@ -535,7 +553,7 @@ void guest_set_pte(struct lguest *lg, } /*H:400 - * (iii) Setting up a page table entry when the Guest tells us it has changed. + * (iii) Setting up a page table entry when the Guest tells us one has changed. * * Just like we did in interrupts_and_traps.c, it makes sense for us to deal * with the other side of page tables while we're here: what happens when the @@ -612,9 +630,10 @@ void free_guest_pagetable(struct lguest *lg) /*H:480 (vi) Mapping the Switcher when the Guest is about to run. * - * The Switcher and the two pages for this CPU need to be available to the + * The Switcher and the two pages for this CPU need to be visible in the * Guest (and not the pages for other CPUs). We have the appropriate PTE pages - * for each CPU already set up, we just need to hook them in. */ + * for each CPU already set up, we just need to hook them in now we know which + * Guest is about to run on this CPU. */ void map_switcher_in_guest(struct lguest *lg, struct lguest_pages *pages) { pte_t *switcher_pte_page = __get_cpu_var(switcher_pte_pages); @@ -677,6 +696,18 @@ static __init void populate_switcher_pte_page(unsigned int cpu, __pgprot(_PAGE_PRESENT|_PAGE_ACCESSED)); } +/* We've made it through the page table code. Perhaps our tired brains are + * still processing the details, or perhaps we're simply glad it's over. + * + * If nothing else, note that all this complexity in juggling shadow page + * tables in sync with the Guest's page tables is for one reason: for most + * Guests this page table dance determines how bad performance will be. This + * is why Xen uses exotic direct Guest pagetable manipulation, and why both + * Intel and AMD have implemented shadow page table support directly into + * hardware. + * + * There is just one file remaining in the Host. */ + /*H:510 At boot or module load time, init_pagetables() allocates and populates * the Switcher PTE page for each CPU. */ __init int init_pagetables(struct page **switcher_page, unsigned int pages) diff --git a/drivers/lguest/segments.c b/drivers/lguest/segments.c index c2434ec99f7..9e189cbec7d 100644 --- a/drivers/lguest/segments.c +++ b/drivers/lguest/segments.c @@ -12,8 +12,6 @@ #include "lg.h" /*H:600 - * We've almost completed the Host; there's just one file to go! - * * Segments & The Global Descriptor Table * * (That title sounds like a bad Nerdcore group. Not to suggest that there are @@ -55,7 +53,7 @@ static int ignored_gdt(unsigned int num) || num == GDT_ENTRY_DOUBLEFAULT_TSS); } -/*H:610 Once the GDT has been changed, we fix the new entries up a little. We +/*H:630 Once the Guest gave us new GDT entries, we fix them up a little. We * don't care if they're invalid: the worst that can happen is a General * Protection Fault in the Switcher when it restores a Guest segment register * which tries to use that entry. Then we kill the Guest for causing such a @@ -84,25 +82,33 @@ static void fixup_gdt_table(struct lguest *lg, unsigned start, unsigned end) } } -/* This routine is called at boot or modprobe time for each CPU to set up the - * "constant" GDT entries for Guests running on that CPU. */ +/*H:610 Like the IDT, we never simply use the GDT the Guest gives us. We keep + * a GDT for each CPU, and copy across the Guest's entries each time we want to + * run the Guest on that CPU. + * + * This routine is called at boot or modprobe time for each CPU to set up the + * constant GDT entries: the ones which are the same no matter what Guest we're + * running. */ void setup_default_gdt_entries(struct lguest_ro_state *state) { struct desc_struct *gdt = state->guest_gdt; unsigned long tss = (unsigned long)&state->guest_tss; - /* The hypervisor segments are full 0-4G segments, privilege level 0 */ + /* The Switcher segments are full 0-4G segments, privilege level 0 */ gdt[GDT_ENTRY_LGUEST_CS] = FULL_EXEC_SEGMENT; gdt[GDT_ENTRY_LGUEST_DS] = FULL_SEGMENT; - /* The TSS segment refers to the TSS entry for this CPU, so we cannot - * copy it from the Guest. Forgive the magic flags */ + /* The TSS segment refers to the TSS entry for this particular CPU. + * Forgive the magic flags: the 0x8900 means the entry is Present, it's + * privilege level 0 Available 386 TSS system segment, and the 0x67 + * means Saturn is eclipsed by Mercury in the twelfth house. */ gdt[GDT_ENTRY_TSS].a = 0x00000067 | (tss << 16); gdt[GDT_ENTRY_TSS].b = 0x00008900 | (tss & 0xFF000000) | ((tss >> 16) & 0x000000FF); } -/* This routine is called before the Guest is run for the first time. */ +/* This routine sets up the initial Guest GDT for booting. All entries start + * as 0 (unusable). */ void setup_guest_gdt(struct lguest *lg) { /* Start with full 0-4G segments... */ @@ -114,13 +120,8 @@ void setup_guest_gdt(struct lguest *lg) lg->arch.gdt[GDT_ENTRY_KERNEL_DS].b |= (GUEST_PL << 13); } -/* Like the IDT, we never simply use the GDT the Guest gives us. We set up the - * GDTs for each CPU, then we copy across the entries each time we want to run - * a different Guest on that CPU. */ - -/* A partial GDT load, for the three "thead-local storage" entries. Otherwise - * it's just like load_guest_gdt(). So much, in fact, it would probably be - * neater to have a single hypercall to cover both. */ +/*H:650 An optimization of copy_gdt(), for just the three "thead-local storage" + * entries. */ void copy_gdt_tls(const struct lguest *lg, struct desc_struct *gdt) { unsigned int i; @@ -129,7 +130,9 @@ void copy_gdt_tls(const struct lguest *lg, struct desc_struct *gdt) gdt[i] = lg->arch.gdt[i]; } -/* This is the full version */ +/*H:640 When the Guest is run on a different CPU, or the GDT entries have + * changed, copy_gdt() is called to copy the Guest's GDT entries across to this + * CPU's GDT. */ void copy_gdt(const struct lguest *lg, struct desc_struct *gdt) { unsigned int i; @@ -141,7 +144,8 @@ void copy_gdt(const struct lguest *lg, struct desc_struct *gdt) gdt[i] = lg->arch.gdt[i]; } -/* This is where the Guest asks us to load a new GDT (LHCALL_LOAD_GDT). */ +/*H:620 This is where the Guest asks us to load a new GDT (LHCALL_LOAD_GDT). + * We copy it from the Guest and tweak the entries. */ void load_guest_gdt(struct lguest *lg, unsigned long table, u32 num) { /* We assume the Guest has the same number of GDT entries as the @@ -157,16 +161,22 @@ void load_guest_gdt(struct lguest *lg, unsigned long table, u32 num) lg->changed |= CHANGED_GDT; } +/* This is the fast-track version for just changing the three TLS entries. + * Remember that this happens on every context switch, so it's worth + * optimizing. But wouldn't it be neater to have a single hypercall to cover + * both cases? */ void guest_load_tls(struct lguest *lg, unsigned long gtls) { struct desc_struct *tls = &lg->arch.gdt[GDT_ENTRY_TLS_MIN]; __lgread(lg, tls, gtls, sizeof(*tls)*GDT_ENTRY_TLS_ENTRIES); fixup_gdt_table(lg, GDT_ENTRY_TLS_MIN, GDT_ENTRY_TLS_MAX+1); + /* Note that just the TLS entries have changed. */ lg->changed |= CHANGED_GDT_TLS; } +/*:*/ -/* +/*H:660 * With this, we have finished the Host. * * Five of the seven parts of our task are complete. You have made it through diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c index 09d9207420d..482aec2a963 100644 --- a/drivers/lguest/x86/core.c +++ b/drivers/lguest/x86/core.c @@ -63,7 +63,7 @@ static struct lguest_pages *lguest_pages(unsigned int cpu) static DEFINE_PER_CPU(struct lguest *, last_guest); /*S:010 - * We are getting close to the Switcher. + * We approach the Switcher. * * Remember that each CPU has two pages which are visible to the Guest when it * runs on that CPU. This has to contain the state for that Guest: we copy the @@ -134,7 +134,7 @@ static void run_guest_once(struct lguest *lg, struct lguest_pages *pages) * * The lcall also pushes the old code segment (KERNEL_CS) onto the * stack, then the address of this call. This stack layout happens to - * exactly match the stack of an interrupt... */ + * exactly match the stack layout created by an interrupt... */ asm volatile("pushf; lcall *lguest_entry" /* This is how we tell GCC that %eax ("a") and %ebx ("b") * are changed by this routine. The "=" means output. */ @@ -151,40 +151,46 @@ static void run_guest_once(struct lguest *lg, struct lguest_pages *pages) } /*:*/ +/*M:002 There are hooks in the scheduler which we can register to tell when we + * get kicked off the CPU (preempt_notifier_register()). This would allow us + * to lazily disable SYSENTER which would regain some performance, and should + * also simplify copy_in_guest_info(). Note that we'd still need to restore + * things when we exit to Launcher userspace, but that's fairly easy. + * + * The hooks were designed for KVM, but we can also put them to good use. :*/ + /*H:040 This is the i386-specific code to setup and run the Guest. Interrupts * are disabled: we own the CPU. */ void lguest_arch_run_guest(struct lguest *lg) { - /* Remember the awfully-named TS bit? If the Guest has asked - * to set it we set it now, so we can trap and pass that trap - * to the Guest if it uses the FPU. */ + /* Remember the awfully-named TS bit? If the Guest has asked to set it + * we set it now, so we can trap and pass that trap to the Guest if it + * uses the FPU. */ if (lg->ts) lguest_set_ts(); - /* SYSENTER is an optimized way of doing system calls. We - * can't allow it because it always jumps to privilege level 0. - * A normal Guest won't try it because we don't advertise it in - * CPUID, but a malicious Guest (or malicious Guest userspace - * program) could, so we tell the CPU to disable it before - * running the Guest. */ + /* SYSENTER is an optimized way of doing system calls. We can't allow + * it because it always jumps to privilege level 0. A normal Guest + * won't try it because we don't advertise it in CPUID, but a malicious + * Guest (or malicious Guest userspace program) could, so we tell the + * CPU to disable it before running the Guest. */ if (boot_cpu_has(X86_FEATURE_SEP)) wrmsr(MSR_IA32_SYSENTER_CS, 0, 0); - /* Now we actually run the Guest. It will pop back out when - * something interesting happens, and we can examine its - * registers to see what it was doing. */ + /* Now we actually run the Guest. It will return when something + * interesting happens, and we can examine its registers to see what it + * was doing. */ run_guest_once(lg, lguest_pages(raw_smp_processor_id())); - /* The "regs" pointer contains two extra entries which are not - * really registers: a trap number which says what interrupt or - * trap made the switcher code come back, and an error code - * which some traps set. */ + /* Note that the "regs" pointer contains two extra entries which are + * not really registers: a trap number which says what interrupt or + * trap made the switcher code come back, and an error code which some + * traps set. */ - /* If the Guest page faulted, then the cr2 register will tell - * us the bad virtual address. We have to grab this now, - * because once we re-enable interrupts an interrupt could - * fault and thus overwrite cr2, or we could even move off to a - * different CPU. */ + /* If the Guest page faulted, then the cr2 register will tell us the + * bad virtual address. We have to grab this now, because once we + * re-enable interrupts an interrupt could fault and thus overwrite + * cr2, or we could even move off to a different CPU. */ if (lg->regs->trapnum == 14) lg->arch.last_pagefault = read_cr2(); /* Similarly, if we took a trap because the Guest used the FPU, @@ -197,14 +203,15 @@ void lguest_arch_run_guest(struct lguest *lg) wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0); } -/*H:130 Our Guest is usually so well behaved; it never tries to do things it - * isn't allowed to. Unfortunately, Linux's paravirtual infrastructure isn't - * quite complete, because it doesn't contain replacements for the Intel I/O - * instructions. As a result, the Guest sometimes fumbles across one during - * the boot process as it probes for various things which are usually attached - * to a PC. +/*H:130 Now we've examined the hypercall code; our Guest can make requests. + * Our Guest is usually so well behaved; it never tries to do things it isn't + * allowed to, and uses hypercalls instead. Unfortunately, Linux's paravirtual + * infrastructure isn't quite complete, because it doesn't contain replacements + * for the Intel I/O instructions. As a result, the Guest sometimes fumbles + * across one during the boot process as it probes for various things which are + * usually attached to a PC. * - * When the Guest uses one of these instructions, we get trap #13 (General + * When the Guest uses one of these instructions, we get a trap (General * Protection Fault) and come here. We see if it's one of those troublesome * instructions and skip over it. We return true if we did. */ static int emulate_insn(struct lguest *lg) @@ -275,43 +282,43 @@ static int emulate_insn(struct lguest *lg) void lguest_arch_handle_trap(struct lguest *lg) { switch (lg->regs->trapnum) { - case 13: /* We've intercepted a GPF. */ - /* Check if this was one of those annoying IN or OUT - * instructions which we need to emulate. If so, we - * just go back into the Guest after we've done it. */ + case 13: /* We've intercepted a General Protection Fault. */ + /* Check if this was one of those annoying IN or OUT + * instructions which we need to emulate. If so, we just go + * back into the Guest after we've done it. */ if (lg->regs->errcode == 0) { if (emulate_insn(lg)) return; } break; - case 14: /* We've intercepted a page fault. */ - /* The Guest accessed a virtual address that wasn't - * mapped. This happens a lot: we don't actually set - * up most of the page tables for the Guest at all when - * we start: as it runs it asks for more and more, and - * we set them up as required. In this case, we don't - * even tell the Guest that the fault happened. - * - * The errcode tells whether this was a read or a - * write, and whether kernel or userspace code. */ + case 14: /* We've intercepted a Page Fault. */ + /* The Guest accessed a virtual address that wasn't mapped. + * This happens a lot: we don't actually set up most of the + * page tables for the Guest at all when we start: as it runs + * it asks for more and more, and we set them up as + * required. In this case, we don't even tell the Guest that + * the fault happened. + * + * The errcode tells whether this was a read or a write, and + * whether kernel or userspace code. */ if (demand_page(lg, lg->arch.last_pagefault, lg->regs->errcode)) return; - /* OK, it's really not there (or not OK): the Guest - * needs to know. We write out the cr2 value so it - * knows where the fault occurred. - * - * Note that if the Guest were really messed up, this - * could happen before it's done the INITIALIZE - * hypercall, so lg->lguest_data will be NULL */ + /* OK, it's really not there (or not OK): the Guest needs to + * know. We write out the cr2 value so it knows where the + * fault occurred. + * + * Note that if the Guest were really messed up, this could + * happen before it's done the LHCALL_LGUEST_INIT hypercall, so + * lg->lguest_data could be NULL */ if (lg->lguest_data && put_user(lg->arch.last_pagefault, &lg->lguest_data->cr2)) kill_guest(lg, "Writing cr2"); break; case 7: /* We've intercepted a Device Not Available fault. */ - /* If the Guest doesn't want to know, we already - * restored the Floating Point Unit, so we just - * continue without telling it. */ + /* If the Guest doesn't want to know, we already restored the + * Floating Point Unit, so we just continue without telling + * it. */ if (!lg->ts) return; break; @@ -536,9 +543,6 @@ int lguest_arch_init_hypercalls(struct lguest *lg) return 0; } -/* Now we've examined the hypercall code; our Guest can make requests. There - * is one other way we can do things for the Guest, as we see in - * emulate_insn(). :*/ /*L:030 lguest_arch_setup_regs() * @@ -570,8 +574,8 @@ void lguest_arch_setup_regs(struct lguest *lg, unsigned long start) /* %esi points to our boot information, at physical address 0, so don't * touch it. */ + /* There are a couple of GDT entries the Guest expects when first * booting. */ - setup_guest_gdt(lg); } diff --git a/drivers/lguest/x86/switcher_32.S b/drivers/lguest/x86/switcher_32.S index 1010b90b11f..0af8baaa0d4 100644 --- a/drivers/lguest/x86/switcher_32.S +++ b/drivers/lguest/x86/switcher_32.S @@ -6,6 +6,37 @@ * are feeling invigorated and refreshed then the next, more challenging stage * can be found in "make Guest". :*/ +/*M:012 Lguest is meant to be simple: my rule of thumb is that 1% more LOC must + * gain at least 1% more performance. Since neither LOC nor performance can be + * measured beforehand, it generally means implementing a feature then deciding + * if it's worth it. And once it's implemented, who can say no? + * + * This is why I haven't implemented this idea myself. I want to, but I + * haven't. You could, though. + * + * The main place where lguest performance sucks is Guest page faulting. When + * a Guest userspace process hits an unmapped page we switch back to the Host, + * walk the page tables, find it's not mapped, switch back to the Guest page + * fault handler, which calls a hypercall to set the page table entry, then + * finally returns to userspace. That's two round-trips. + * + * If we had a small walker in the Switcher, we could quickly check the Guest + * page table and if the page isn't mapped, immediately reflect the fault back + * into the Guest. This means the Switcher would have to know the top of the + * Guest page table and the page fault handler address. + * + * For simplicity, the Guest should only handle the case where the privilege + * level of the fault is 3 and probably only not present or write faults. It + * should also detect recursive faults, and hand the original fault to the + * Host (which is actually really easy). + * + * Two questions remain. Would the performance gain outweigh the complexity? + * And who would write the verse documenting it? :*/ + +/*M:011 Lguest64 handles NMI. This gave me NMI envy (until I looked at their + * code). It's worth doing though, since it would let us use oprofile in the + * Host when a Guest is running. :*/ + /*S:100 * Welcome to the Switcher itself! * @@ -88,7 +119,7 @@ ENTRY(switch_to_guest) // All saved and there's now five steps before us: // Stack, GDT, IDT, TSS - // And last of all the page tables are flipped. + // Then last of all the page tables are flipped. // Yet beware that our stack pointer must be // Always valid lest an NMI hits @@ -103,25 +134,25 @@ ENTRY(switch_to_guest) lgdt LGUEST_PAGES_guest_gdt_desc(%eax) // The Guest's IDT we did partially - // Move to the "struct lguest_pages" as well. + // Copy to "struct lguest_pages" as well. lidt LGUEST_PAGES_guest_idt_desc(%eax) // The TSS entry which controls traps // Must be loaded up with "ltr" now: + // The GDT entry that TSS uses + // Changes type when we load it: damn Intel! // For after we switch over our page tables - // It (as the rest) will be writable no more. - // (The GDT entry TSS needs - // Changes type when we load it: damn Intel!) + // That entry will be read-only: we'd crash. movl $(GDT_ENTRY_TSS*8), %edx ltr %dx // Look back now, before we take this last step! // The Host's TSS entry was also marked used; - // Let's clear it again, ere we return. + // Let's clear it again for our return. // The GDT descriptor of the Host // Points to the table after two "size" bytes movl (LGUEST_PAGES_host_gdt_desc+2)(%eax), %edx - // Clear the type field of "used" (byte 5, bit 2) + // Clear "used" from type field (byte 5, bit 2) andb $0xFD, (GDT_ENTRY_TSS*8 + 5)(%edx) // Once our page table's switched, the Guest is live! @@ -131,7 +162,7 @@ ENTRY(switch_to_guest) // The page table change did one tricky thing: // The Guest's register page has been mapped - // Writable onto our %esp (stack) -- + // Writable under our %esp (stack) -- // We can simply pop off all Guest regs. popl %eax popl %ebx @@ -152,16 +183,15 @@ ENTRY(switch_to_guest) addl $8, %esp // The last five stack slots hold return address - // And everything needed to change privilege - // Into the Guest privilege level of 1, + // And everything needed to switch privilege + // From Switcher's level 0 to Guest's 1, // And the stack where the Guest had last left it. // Interrupts are turned back on: we are Guest. iret -// There are two paths where we switch to the Host +// We treat two paths to switch back to the Host +// Yet both must save Guest state and restore Host // So we put the routine in a macro. -// We are on our way home, back to the Host -// Interrupted out of the Guest, we come here. #define SWITCH_TO_HOST \ /* We save the Guest state: all registers first \ * Laid out just as "struct lguest_regs" defines */ \ @@ -194,7 +224,7 @@ ENTRY(switch_to_guest) movl %esp, %eax; \ andl $(~(1 << PAGE_SHIFT - 1)), %eax; \ /* Save our trap number: the switch will obscure it \ - * (The Guest regs are not mapped here in the Host) \ + * (In the Host the Guest regs are not mapped here) \ * %ebx holds it safe for deliver_to_host */ \ movl LGUEST_PAGES_regs_trapnum(%eax), %ebx; \ /* The Host GDT, IDT and stack! \ @@ -210,9 +240,9 @@ ENTRY(switch_to_guest) /* Switch to Host's GDT, IDT. */ \ lgdt LGUEST_PAGES_host_gdt_desc(%eax); \ lidt LGUEST_PAGES_host_idt_desc(%eax); \ - /* Restore the Host's stack where it's saved regs lie */ \ + /* Restore the Host's stack where its saved regs lie */ \ movl LGUEST_PAGES_host_sp(%eax), %esp; \ - /* Last the TSS: our Host is complete */ \ + /* Last the TSS: our Host is returned */ \ movl $(GDT_ENTRY_TSS*8), %edx; \ ltr %dx; \ /* Restore now the regs saved right at the first. */ \ @@ -222,14 +252,15 @@ ENTRY(switch_to_guest) popl %ds; \ popl %es -// Here's where we come when the Guest has just trapped: -// (Which trap we'll see has been pushed on the stack). +// The first path is trod when the Guest has trapped: +// (Which trap it was has been pushed on the stack). // We need only switch back, and the Host will decode // Why we came home, and what needs to be done. return_to_host: SWITCH_TO_HOST iret +// We are lead to the second path like so: // An interrupt, with some cause external // Has ajerked us rudely from the Guest's code // Again we must return home to the Host @@ -238,7 +269,7 @@ deliver_to_host: // But now we must go home via that place // Where that interrupt was supposed to go // Had we not been ensconced, running the Guest. - // Here we see the cleverness of our stack: + // Here we see the trickness of run_guest_once(): // The Host stack is formed like an interrupt // With EIP, CS and EFLAGS layered. // Interrupt handlers end with "iret" @@ -263,7 +294,7 @@ deliver_to_host: xorw %ax, %ax orl %eax, %edx // Now the address of the handler's in %edx - // We call it now: its "iret" takes us home. + // We call it now: its "iret" drops us home. jmp *%edx // Every interrupt can come to us here |