[PATCH 10/33] KVM: MMU: Write protect guest pages when a shadow is created for them

Avi Kivity
2007-01-04T15:59:06Z

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-atKUWr5tajBWk0Htik3J/w@public.gmane.org>

Index: linux-2.6/drivers/kvm/mmu.c
===================================================================
--- linux-2.6.orig/drivers/kvm/mmu.c
+++ linux-2.6/drivers/kvm/mmu.c
@@ -274,6 +274,35 @@ static void rmap_remove(struct kvm *kvm,
}
}

+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->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

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
*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
*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,
Index: linux-2.6/drivers/kvm/paging_tmpl.h
===================================================================
--- linux-2.6.orig/drivers/kvm/paging_tmpl.h
+++ linux-2.6/drivers/kvm/paging_tmpl.h
@@ -133,6 +133,7 @@ static void FNAME(walk_addr)(struct gues
walker->level - 1, table_gfn);
}
walker->ptep = ptep;
+ pgprintk("%s: pte %llx\n", __FUNCTION__, (u64)*ptep);
}

static void FNAME(release_walker)(struct guest_walker *walker)