KVM: MMU: Fix hugepage pdes mapping same physical address with different access

The kvm mmu keeps a shadow page for hugepage pdes; if several such pdes map
the same physical address, they share the same shadow page.  This is a fairly
common case (kernel mappings on i386 nonpae Linux, for example).

However, if the two pdes map the same memory but with different permissions, kvm
will happily use the cached shadow page.  If the access through the more
permissive pde will occur after the access to the strict pde, an endless pagefault
loop will be generated and the guest will make no progress.

Fix by making the access permissions part of the cache lookup key.

The fix allows Xen pae to boot on kvm and run guest domains.

Thanks to Jeremy Fitzhardinge for reporting the bug and testing the fix.

Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/drivers/kvm/mmu.c b/drivers/kvm/mmu.c
index 2930d7cc7c0..c738fb1cea3 100644
--- a/drivers/kvm/mmu.c
+++ b/drivers/kvm/mmu.c
@@ -568,6 +568,7 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
 					     gva_t gaddr,
 					     unsigned level,
 					     int metaphysical,
+					     unsigned hugepage_access,
 					     u64 *parent_pte)
 {
 	union kvm_mmu_page_role role;
@@ -581,6 +582,7 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
 	role.glevels = vcpu->mmu.root_level;
 	role.level = level;
 	role.metaphysical = metaphysical;
+	role.hugepage_access = hugepage_access;
 	if (vcpu->mmu.root_level <= PT32_ROOT_LEVEL) {
 		quadrant = gaddr >> (PAGE_SHIFT + (PT64_PT_BITS * level));
 		quadrant &= (1 << ((PT32_PT_BITS - PT64_PT_BITS) * level)) - 1;
@@ -780,7 +782,7 @@ static int nonpaging_map(struct kvm_vcpu *vcpu, gva_t v, hpa_t p)
 				>> PAGE_SHIFT;
 			new_table = kvm_mmu_get_page(vcpu, pseudo_gfn,
 						     v, level - 1,
-						     1, &table[index]);
+						     1, 0, &table[index]);
 			if (!new_table) {
 				pgprintk("nonpaging_map: ENOMEM\n");
 				return -ENOMEM;
@@ -835,7 +837,7 @@ static void mmu_alloc_roots(struct kvm_vcpu *vcpu)
 
 		ASSERT(!VALID_PAGE(root));
 		page = kvm_mmu_get_page(vcpu, root_gfn, 0,
-					PT64_ROOT_LEVEL, 0, NULL);
+					PT64_ROOT_LEVEL, 0, 0, NULL);
 		root = page->page_hpa;
 		++page->root_count;
 		vcpu->mmu.root_hpa = root;
@@ -852,7 +854,7 @@ static void mmu_alloc_roots(struct kvm_vcpu *vcpu)
 			root_gfn = 0;
 		page = kvm_mmu_get_page(vcpu, root_gfn, i << 30,
 					PT32_ROOT_LEVEL, !is_paging(vcpu),
-					NULL);
+					0, NULL);
 		root = page->page_hpa;
 		++page->root_count;
 		vcpu->mmu.pae_root[i] = root | PT_PRESENT_MASK;