[PATCH] KVM: MMU: Zap shadow page table entries on writes to guest page tables

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>

1 files changed, 36 insertions, 0 deletions

diff --git a/drivers/kvm/mmu.c b/drivers/kvm/mmu.c
index bce7eb21f739..6dbd83b86623 100644
--- a/drivers/kvm/mmu.c
+++ b/drivers/kvm/mmu.c
@@ -958,7 +958,43 @@ int kvm_mmu_reset_context(struct kvm_vcpu *vcpu)
 
 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_head *bucket;
+        unsigned index;
+        u64 *spte;
+        u64 pte;
+        unsigned offset = offset_in_page(gpa);
+        unsigned page_offset;
+        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) {
+                if (page->gfn != gfn || page->role.metaphysical)
+                        continue;
+                page_offset = offset;
+                level = page->role.level;
+                if (page->role.glevels == PT32_ROOT_LEVEL) {
+                        page_offset <<= 1;          /* 32->64 */
+                        page_offset &= ~PAGE_MASK;
+                }
+                spte = __va(page->page_hpa);
+                spte += page_offset / sizeof(*spte);
+                pte = *spte;
+                if (is_present_pte(pte)) {
+                        if (level == PT_PAGE_TABLE_LEVEL)
+                                rmap_remove(vcpu->kvm, spte);
+                        else {
+                                child = page_header(pte & PT64_BASE_ADDR_MASK);
+                                mmu_page_remove_parent_pte(child, spte);
+                        }
+                }
+                *spte = 0;
+        }
 }
 
 void kvm_mmu_post_write(struct kvm_vcpu *vcpu, gpa_t gpa, int bytes)