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Commit 0e7bc4b9 authored by Avi Kivity's avatar Avi Kivity Committed by Linus Torvalds
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[PATCH] KVM: MMU: Handle misaligned accesses to write protected guest page 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: default avatarAvi Kivity <avi@qumranet.com>
Acked-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 73f7198e
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+17 −2
Original line number Diff line number Diff line
@@ -954,21 +954,36 @@ void kvm_mmu_pre_write(struct kvm_vcpu *vcpu, gpa_t gpa, int bytes)
	gfn_t gfn = gpa >> PAGE_SHIFT;
	struct kvm_mmu_page *page;
	struct kvm_mmu_page *child;
	struct hlist_node *node;
	struct hlist_node *node, *n;
	struct hlist_head *bucket;
	unsigned index;
	u64 *spte;
	u64 pte;
	unsigned offset = offset_in_page(gpa);
	unsigned pte_size;
	unsigned page_offset;
	unsigned misaligned;
	int level;

	pgprintk("%s: gpa %llx bytes %d\n", __FUNCTION__, gpa, bytes);
	index = kvm_page_table_hashfn(gfn) % KVM_NUM_MMU_PAGES;
	bucket = &vcpu->kvm->mmu_page_hash[index];
	hlist_for_each_entry(page, node, bucket, hash_link) {
	hlist_for_each_entry_safe(page, node, n, bucket, hash_link) {
		if (page->gfn != gfn || page->role.metaphysical)
			continue;
		pte_size = page->role.glevels == PT32_ROOT_LEVEL ? 4 : 8;
		misaligned = (offset ^ (offset + bytes - 1)) & ~(pte_size - 1);
		if (misaligned) {
			/*
			 * Misaligned accesses are too much trouble to fix
			 * up; also, they usually indicate a page is not used
			 * as a page table.
			 */
			pgprintk("misaligned: gpa %llx bytes %d role %x\n",
				 gpa, bytes, page->role.word);
			kvm_mmu_zap_page(vcpu, page);
			continue;
		}
		page_offset = offset;
		level = page->role.level;
		if (page->role.glevels == PT32_ROOT_LEVEL) {