access_process_vm device memory infrastructure

In order to be able to debug things like the X server and programs using
the PPC Cell SPUs, the debugger needs to be able to access device memory
through ptrace and /proc/pid/mem.

This patch:

Add the generic_access_phys access function and put the hooks in place
to allow access_process_vm to access device or PPC Cell SPU memory.

[riel@redhat.com: Add documentation for the vm_ops->access function]
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Benjamin Herrensmidt <benh@kernel.crashing.org>
Cc: Dave Airlie <airlied@linux.ie>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 113 insertions, 18 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 46dbed4b744..87350321e66 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2751,6 +2751,86 @@ int in_gate_area_no_task(unsigned long addr)
 
 #endif	/* __HAVE_ARCH_GATE_AREA */
 
+#ifdef CONFIG_HAVE_IOREMAP_PROT
+static resource_size_t follow_phys(struct vm_area_struct *vma,
+			unsigned long address, unsigned int flags,
+			unsigned long *prot)
+{
+	pgd_t *pgd;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *ptep, pte;
+	spinlock_t *ptl;
+	resource_size_t phys_addr = 0;
+	struct mm_struct *mm = vma->vm_mm;
+
+	VM_BUG_ON(!(vma->vm_flags & (VM_IO | VM_PFNMAP)));
+
+	pgd = pgd_offset(mm, address);
+	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
+		goto no_page_table;
+
+	pud = pud_offset(pgd, address);
+	if (pud_none(*pud) || unlikely(pud_bad(*pud)))
+		goto no_page_table;
+
+	pmd = pmd_offset(pud, address);
+	if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
+		goto no_page_table;
+
+	/* We cannot handle huge page PFN maps. Luckily they don't exist. */
+	if (pmd_huge(*pmd))
+		goto no_page_table;
+
+	ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
+	if (!ptep)
+		goto out;
+
+	pte = *ptep;
+	if (!pte_present(pte))
+		goto unlock;
+	if ((flags & FOLL_WRITE) && !pte_write(pte))
+		goto unlock;
+	phys_addr = pte_pfn(pte);
+	phys_addr <<= PAGE_SHIFT; /* Shift here to avoid overflow on PAE */
+
+	*prot = pgprot_val(pte_pgprot(pte));
+
+unlock:
+	pte_unmap_unlock(ptep, ptl);
+out:
+	return phys_addr;
+no_page_table:
+	return 0;
+}
+
+int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
+			void *buf, int len, int write)
+{
+	resource_size_t phys_addr;
+	unsigned long prot = 0;
+	void *maddr;
+	int offset = addr & (PAGE_SIZE-1);
+
+	if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
+		return -EINVAL;
+
+	phys_addr = follow_phys(vma, addr, write, &prot);
+
+	if (!phys_addr)
+		return -EINVAL;
+
+	maddr = ioremap_prot(phys_addr, PAGE_SIZE, prot);
+	if (write)
+		memcpy_toio(maddr + offset, buf, len);
+	else
+		memcpy_fromio(buf, maddr + offset, len);
+	iounmap(maddr);
+
+	return len;
+}
+#endif
+
 /*
  * Access another process' address space.
  * Source/target buffer must be kernel space,
@@ -2760,7 +2840,6 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, in
 {
 	struct mm_struct *mm;
 	struct vm_area_struct *vma;
-	struct page *page;
 	void *old_buf = buf;
 
 	mm = get_task_mm(tsk);
@@ -2772,28 +2851,44 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, in
 	while (len) {
 		int bytes, ret, offset;
 		void *maddr;
+		struct page *page = NULL;
 
 		ret = get_user_pages(tsk, mm, addr, 1,
 				write, 1, &page, &vma);
-		if (ret <= 0)
-			break;
-
-		bytes = len;
-		offset = addr & (PAGE_SIZE-1);
-		if (bytes > PAGE_SIZE-offset)
-			bytes = PAGE_SIZE-offset;
-
-		maddr = kmap(page);
-		if (write) {
-			copy_to_user_page(vma, page, addr,
-					  maddr + offset, buf, bytes);
-			set_page_dirty_lock(page);
+		if (ret <= 0) {
+			/*
+			 * Check if this is a VM_IO | VM_PFNMAP VMA, which
+			 * we can access using slightly different code.
+			 */
+#ifdef CONFIG_HAVE_IOREMAP_PROT
+			vma = find_vma(mm, addr);
+			if (!vma)
+				break;
+			if (vma->vm_ops && vma->vm_ops->access)
+				ret = vma->vm_ops->access(vma, addr, buf,
+							  len, write);
+			if (ret <= 0)
+#endif
+				break;
+			bytes = ret;
 		} else {
-			copy_from_user_page(vma, page, addr,
-					    buf, maddr + offset, bytes);
+			bytes = len;
+			offset = addr & (PAGE_SIZE-1);
+			if (bytes > PAGE_SIZE-offset)
+				bytes = PAGE_SIZE-offset;
+
+			maddr = kmap(page);
+			if (write) {
+				copy_to_user_page(vma, page, addr,
+						  maddr + offset, buf, bytes);
+				set_page_dirty_lock(page);
+			} else {
+				copy_from_user_page(vma, page, addr,
+						    buf, maddr + offset, bytes);
+			}
+			kunmap(page);
+			page_cache_release(page);
 		}
-		kunmap(page);
-		page_cache_release(page);
 		len -= bytes;
 		buf += bytes;
 		addr += bytes;