[PATCH] KVM: MMU: Write protect guest pages when a shadow is created for them

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>

1 files changed, 54 insertions, 18 deletions

diff --git a/drivers/kvm/mmu.c b/drivers/kvm/mmu.c
index 47c699c21c08..ba813f49f8aa 100644
--- a/drivers/kvm/mmu.c
+++ b/drivers/kvm/mmu.c
@@ -274,6 +274,35 @@ static void rmap_remove(struct kvm *kvm, u64 *spte)
         }
 }
 
+static void rmap_write_protect(struct kvm *kvm, u64 gfn)
+{
+        struct page *page;
+        struct kvm_memory_slot *slot;
+        struct kvm_rmap_desc *desc;
+        u64 *spte;
+
+        slot = gfn_to_memslot(kvm, gfn);
+        BUG_ON(!slot);
+        page = gfn_to_page(slot, gfn);
+
+        while (page->private) {
+                if (!(page->private & 1))
+                        spte = (u64 *)page->private;
+                else {
+                        desc = (struct kvm_rmap_desc *)(page->private & ~1ul);
+                        spte = desc->shadow_ptes[0];
+                }
+                BUG_ON(!spte);
+                BUG_ON((*spte & PT64_BASE_ADDR_MASK) !=
+                       page_to_pfn(page) << PAGE_SHIFT);
+                BUG_ON(!(*spte & PT_PRESENT_MASK));
+                BUG_ON(!(*spte & PT_WRITABLE_MASK));
+                rmap_printk("rmap_write_protect: spte %p %llx\n", spte, *spte);
+                rmap_remove(kvm, spte);
+                *spte &= ~(u64)PT_WRITABLE_MASK;
+        }
+}
+
 static void kvm_mmu_free_page(struct kvm_vcpu *vcpu, hpa_t page_hpa)
 {
         struct kvm_mmu_page *page_head = page_header(page_hpa);
@@ -444,6 +473,8 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
         page->gfn = gfn;
         page->role = role;
         hlist_add_head(&page->hash_link, bucket);
+        if (!metaphysical)
+                rmap_write_protect(vcpu->kvm, gfn);
         return page;
 }
 
@@ -705,6 +736,7 @@ static void kvm_mmu_flush_tlb(struct kvm_vcpu *vcpu)
 
 static void paging_new_cr3(struct kvm_vcpu *vcpu)
 {
+        pgprintk("%s: cr3 %lx\n", __FUNCTION__, vcpu->cr3);
         mmu_free_roots(vcpu);
         mmu_alloc_roots(vcpu);
         kvm_mmu_flush_tlb(vcpu);
@@ -727,24 +759,11 @@ static inline void set_pte_common(struct kvm_vcpu *vcpu,
         *shadow_pte |= access_bits << PT_SHADOW_BITS_OFFSET;
         if (!dirty)
                 access_bits &= ~PT_WRITABLE_MASK;
-        if (access_bits & PT_WRITABLE_MASK) {
-                struct kvm_mmu_page *shadow;
 
-                shadow = kvm_mmu_lookup_page(vcpu, gaddr >> PAGE_SHIFT);
-                if (shadow)
-                        pgprintk("%s: found shadow page for %lx, marking ro\n",
-                                 __FUNCTION__, (gfn_t)(gaddr >> PAGE_SHIFT));
-                if (shadow)
-                        access_bits &= ~PT_WRITABLE_MASK;
-        }
-
-        if (access_bits & PT_WRITABLE_MASK)
-                mark_page_dirty(vcpu->kvm, gaddr >> PAGE_SHIFT);
+        paddr = gpa_to_hpa(vcpu, gaddr & PT64_BASE_ADDR_MASK);
 
         *shadow_pte |= access_bits;
 
-        paddr = gpa_to_hpa(vcpu, gaddr & PT64_BASE_ADDR_MASK);
-
         if (!(*shadow_pte & PT_GLOBAL_MASK))
                 mark_pagetable_nonglobal(shadow_pte);
 
@@ -752,11 +771,28 @@ static inline void set_pte_common(struct kvm_vcpu *vcpu,
                 *shadow_pte |= gaddr;
                 *shadow_pte |= PT_SHADOW_IO_MARK;
                 *shadow_pte &= ~PT_PRESENT_MASK;
-        } else {
-                *shadow_pte |= paddr;
-                page_header_update_slot(vcpu->kvm, shadow_pte, gaddr);
-                rmap_add(vcpu->kvm, shadow_pte);
+                return;
         }
+
+        *shadow_pte |= paddr;
+
+        if (access_bits & PT_WRITABLE_MASK) {
+                struct kvm_mmu_page *shadow;
+
+                shadow = kvm_mmu_lookup_page(vcpu, gaddr >> PAGE_SHIFT);
+                if (shadow) {
+                        pgprintk("%s: found shadow page for %lx, marking ro\n",
+                                 __FUNCTION__, (gfn_t)(gaddr >> PAGE_SHIFT));
+                        access_bits &= ~PT_WRITABLE_MASK;
+                        *shadow_pte &= ~PT_WRITABLE_MASK;
+                }
+        }
+
+        if (access_bits & PT_WRITABLE_MASK)
+                mark_page_dirty(vcpu->kvm, gaddr >> PAGE_SHIFT);
+
+        page_header_update_slot(vcpu->kvm, shadow_pte, gaddr);
+        rmap_add(vcpu->kvm, shadow_pte);
 }
 
 static void inject_page_fault(struct kvm_vcpu *vcpu,