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path: root/drivers/kvm
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2007-01-11[PATCH] KVM: add VM-exit profilingIngo Molnar
This adds the profile=kvm boot option, which enables KVM to profile VM exits. Use: "readprofile -m ./System.map | sort -n" to see the resulting output: [...] 18246 serial_out 148.3415 18945 native_flush_tlb 378.9000 23618 serial_in 212.7748 29279 __spin_unlock_irq 622.9574 43447 native_apic_write 2068.9048 52702 enable_8259A_irq 742.2817 54250 vgacon_scroll 89.3740 67394 ide_inb 6126.7273 79514 copy_page_range 98.1654 84868 do_wp_page 86.6000 140266 pit_read 783.6089 151436 ide_outb 25239.3333 152668 native_io_delay 21809.7143 174783 mask_and_ack_8259A 783.7803 362404 native_set_pte_at 36240.4000 1688747 total 0.5009 Signed-off-by: Ingo Molnar <mingo@elte.hu> Acked-by: Avi Kivity <avi@qumranet.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: Simplify test for interrupt windowDor Laor
No need to test for rflags.if as both VT and SVM specs assure us that on exit caused from interrupt window opening, 'if' is set. Signed-off-by: Dor Laor <dor.laor@qumranet.com> Signed-off-by: Avi Kivity <avi@qumranet.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: Simplify mmu_alloc_roots()Ingo Molnar
Small optimization/cleanup: page == page_header(page->page_hpa) Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Avi Kivity <avi@qumranet.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: Make loading cr3 more robustIngo Molnar
Prevent the guest's loading of a corrupt cr3 (pointing at no guest phsyical page) from crashing the host. Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Avi Kivity <avi@qumranet.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Add missing dirty bitAvi Kivity
If we emulate a write, we fail to set the dirty bit on the guest pte, leading the guest to believe the page is clean, and thus lose data. Bad. Fix by setting the guest pte dirty bit under such conditions. Signed-off-by: Avi Kivity <avi@qumranet.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: Don't set guest cr3 from vmx_vcpu_setup()Avi Kivity
It overwrites the right cr3 set from mmu setup. Happens only with the test harness. Signed-off-by: Avi Kivity <avi@qumranet.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: Add missing 'break'Avi Kivity
Signed-off-by: Avi Kivity <avi@qumranet.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: Avoid oom on cr3 switchIngo Molnar
Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Avi Kivity <avi@qumranet.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: Initialize vcpu->kvm a little earlierAvi Kivity
Fixes oops on early close of /dev/kvm. Signed-off-by: Avi Kivity <avi@qumranet.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: Improve reporting of vmwrite errorsAvi Kivity
This will allow us to see the root cause when a vmwrite error happens. Signed-off-by: Avi Kivity <avi@qumranet.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: add audit code to check mappings, etc are correctAvi Kivity
Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Destroy mmu while we still have a vcpu leftAvi Kivity
mmu_destroy flushes the guest tlb (indirectly), which needs a valid vcpu. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Flush guest tlb when reducing permissions on a pteAvi Kivity
If we reduce permissions on a pte, we must flush the cached copy of the pte from the guest's tlb. This is implemented at the moment by flushing the entire guest tlb, and can be improved by flushing just the relevant virtual address, if it is known. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Detect oom conditions and propagate error to userspaceAvi Kivity
Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Replace atomic allocations by preallocated objectsAvi Kivity
The mmu sometimes needs memory for reverse mapping and parent pte chains. however, we can't allocate from within the mmu because of the atomic context. So, move the allocations to a central place that can be executed before the main mmu machinery, where we can bail out on failure before any damage is done. (error handling is deffered for now, but the basic structure is there) Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Free pages on kvm destructionAvi Kivity
Because mmu pages have attached rmap and parent pte chain structures, we need to zap them before freeing so the attached structures are freed. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Treat user-mode faults as a hint that a page is no longer ↵Avi Kivity
a page table Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Fix cmpxchg8b emulationAvi Kivity
cmpxchg8b uses edx:eax as the compare operand, not edi:eax. cmpxchg8b is used by 32-bit pae guests to set page table entries atomically, and this is emulated touching shadowed guest page tables. Also, implement it for 32-bit hosts. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Never free a shadow page actively serving as a rootAvi Kivity
We always need cr3 to point to something valid, so if we detect that we're freeing a root page, simply push it back to the top of the active list. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Page table write flood protectionAvi Kivity
In fork() (or when we protect a page that is no longer a page table), we can experience floods of writes to a page, which have to be emulated. This is expensive. So, if we detect such a flood, zap the page so subsequent writes can proceed natively. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: If an empty shadow page is not empty, report more infoAvi Kivity
Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Ensure freed shadow pages are cleanAvi Kivity
Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: <ove is_empty_shadow_page() above kvm_mmu_free_page()Avi Kivity
Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Handle misaligned accesses to write protected guest page ↵Avi Kivity
tables A misaligned access affects two shadow ptes instead of just one. Since a misaligned access is unlikely to occur on a real page table, just zap the page out of existence, avoiding further trouble. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Remove release_pt_page_64()Avi Kivity
Unused. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Remove invlpg interceptionAvi Kivity
Since we write protect shadowed guest page tables, there is no need to trap page invalidations (the guest will always change the mapping before issuing the invlpg instruction). Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: oom handlingAvi Kivity
When beginning to process a page fault, make sure we have enough shadow pages available to service the fault. If not, free some pages. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: kvm_mmu_put_page() only removes one link to the pageAvi Kivity
... and so must not free it unconditionally. Move the freeing to kvm_mmu_zap_page(). Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Implement child shadow unlinkingAvi Kivity
When removing a page table, we must maintain the parent_pte field all child shadow page tables. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: If emulating an instruction fails, try unprotecting the pageAvi Kivity
A page table may have been recycled into a regular page, and so any instruction can be executed on it. Unprotect the page and let the cpu do its thing. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Zap shadow page table entries on writes to guest page tablesAvi Kivity
Iterate over all shadow pages which correspond to a the given guest page table and remove the mappings. A subsequent page fault will reestablish the new mapping. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Support emulated writes into RAMAvi Kivity
As the mmu write protects guest page table, we emulate those writes. Since they are not mmio, there is no need to go to userspace to perform them. So, perform the writes in the kernel if possible, and notify the mmu about them so it can take the approriate action. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Let the walker extract the target page gfn from the pteAvi Kivity
This fixes a problem where set_pte_common() looked for shadowed pages based on the page directory gfn (a huge page) instead of the actual gfn being mapped. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Write protect guest pages when a shadow is created for themAvi Kivity
When we cache a guest page table into a shadow page table, we need to prevent further access to that page by the guest, as that would render the cache incoherent. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Shadow page table cachingAvi Kivity
Define a hashtable for caching shadow page tables. Look up the cache on context switch (cr3 change) or during page faults. The key to the cache is a combination of - the guest page table frame number - the number of paging levels in the guest * we can cache real mode, 32-bit mode, pae, and long mode page tables simultaneously. this is useful for smp bootup. - the guest page table table * some kernels use a page as both a page table and a page directory. this allows multiple shadow pages to exist for that page, one per level - the "quadrant" * 32-bit mode page tables span 4MB, whereas a shadow page table spans 2MB. similarly, a 32-bit page directory spans 4GB, while a shadow page directory spans 1GB. the quadrant allows caching up to 4 shadow page tables for one guest page in one level. - a "metaphysical" bit * for real mode, and for pse pages, there is no guest page table, so set the bit to avoid write protecting the page. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Make kvm_mmu_alloc_page() return a kvm_mmu_page pointerAvi Kivity
This allows further manipulation on the shadow page table. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Make the shadow page tables also special-case paeAvi Kivity
Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Use the guest pdptrs instead of mapping cr3 in pae modeAvi Kivity
This lets us not write protect a partial page, and is anyway what a real processor does. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MU: Special treatment for shadow pae root pagesAvi Kivity
Since we're not going to cache the pae-mode shadow root pages, allocate a single pae shadow that will hold the four lower-level pages, which will act as roots. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Fold fetch_guest() into init_walker()Avi Kivity
It is never necessary to fetch a guest entry from an intermediate page table level (except for large pages), so avoid some confusion by always descending into the lowest possible level. Rename init_walker() to walk_addr() as it is no longer restricted to initialization. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Load the pae pdptrs on cr3 change like the processor doesAvi Kivity
In pae mode, a load of cr3 loads the four third-level page table entries in addition to cr3 itself. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Teach the page table walker to track guest page table gfnsAvi Kivity
Saving the table gfns removes the need to walk the guest and host page tables in lockstep. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: MMU: Implement simple reverse mappingAvi Kivity
Keep in each host page frame's page->private a pointer to the shadow pte which maps it. If there are multiple shadow ptes mapping the page, set bit 0 of page->private, and use the rest as a pointer to a linked list of all such mappings. Reverse mappings are needed because we when we cache shadow page tables, we must protect the guest page tables from being modified by the guest, as that would invalidate the cached ptes. Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: Prevent stale bits in cr0 and cr4Avi Kivity
Hardware virtualization implementations allow the guests to freely change some of the bits in cr0 and cr4, but trap when changing the other bits. This is useful to avoid excessive exits due to changing, for example, the ts flag. It also means the kvm's copy of cr0 and cr4 may be stale with respect to these bits. most of the time this doesn't matter as these bits are not very interesting. Other times, however (for example when returning cr0 to userspace), they are, so get the fresh contents of these bits from the guest by means of a new arch operation. Signed-off-by: Avi Kivity <avi@qumranet.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: Improve interrupt responseDor Laor
The current interrupt injection mechanism might delay an interrupt under the following circumstances: - if injection fails because the guest is not interruptible (rflags.IF clear, or after a 'mov ss' or 'sti' instruction). Userspace can check rflags, but the other cases or not testable under the current API. - if injection fails because of a fault during delivery. This probably never happens under normal guests. - if injection fails due to a physical interrupt causing a vmexit so that it can be handled by the host. In all cases the guest proceeds without processing the interrupt, reducing the interactive feel and interrupt throughput of the guest. This patch fixes the situation by allowing userspace to request an exit when the 'interrupt window' opens, so that it can re-inject the interrupt at the right time. Guest interactivity is very visibly improved. Signed-off-by: Dor Laor <dor.laor@qumranet.com> Signed-off-by: Avi Kivity <avi@qumranet.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: Recover after an arch module load failureYoshimi Ichiyanagi
If we load the wrong arch module, it leaves behind kvm_arch_ops set, which prevents loading of the correct arch module later. Fix be not setting kvm_arch_ops until we're sure it's good. Signed-off-by: Yoshimi Ichiyanagi <ichiyanagi.yoshimi@lab.ntt.co.jp> Signed-off-by: Avi Kivity <avi@qumranet.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: Use raw_smp_processor_id() instead of smp_processor_id() where ↵Ingo Molnar
applicable Signed-off-by: Avi Kivity <avi@qumranet.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2007-01-05[PATCH] KVM: Fix GFP_KERNEL alloc in atomic section bugIngo Molnar
KVM does kmalloc() in an atomic section while having preemption disabled via vcpu_load(). Fix this by moving the ->*_msr setup from the vcpu_setup method to the vcpu_create method. (This is also a small speedup for setting up a vcpu, which can in theory be more frequent than the vcpu_create method). Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Avi Kivity <avi@qumranet.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-12-30[PATCH] kvm: fix GFP_KERNEL allocation in atomic section in ↵Ingo Molnar
kvm_dev_ioctl_create_vcpu() fix an GFP_KERNEL allocation in atomic section: kvm_dev_ioctl_create_vcpu() called kvm_mmu_init(), which calls alloc_pages(), while holding the vcpu. The fix is to set up the MMU state in two phases: kvm_mmu_create() and kvm_mmu_setup(). (NOTE: free_vcpus does an kvm_mmu_destroy() call so there's no need for any extra teardown branch on allocation/init failure here.) Signed-off-by: Ingo Molnar <mingo@elte.hu> Cc: Avi Kivity <avi@qumranet.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-12-30[PATCH] KVM: Fix oops on oomAvi Kivity
__free_page() doesn't like a NULL argument, so check before calling it. A NULL can only happen if memory is exhausted during allocation of a memory slot. Signed-off-by: Avi Kivity <avi@qumranet.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>