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KVM: MMU: Make flooding detection work when guest page faults are bypassed

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When we allow guest page faults to reach the guests directly, we lose
the fault tracking which allows us to detect demand paging.  So we provide
an alternate mechnism by clearing the accessed bit when we set a pte, and
checking it later to see if the guest actually used it.

Signed-off-by: Avi Kivity <avi@qumranet.com>
This commit is contained in:
Avi Kivity 2007-09-23 14:10:49 +02:00
parent c7addb9020
commit 12b7d28fc1
3 changed files with 29 additions and 2 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

1
drivers/kvm/kvm.h
View file

@ -346,6 +346,7 @@ struct kvm_vcpu {
gfn_t last_pt_write_gfn;
int last_pt_write_count;
u64 *last_pte_updated;
struct kvm_guest_debug guest_debug;

21
drivers/kvm/mmu.c
View file

@ -692,6 +692,15 @@ static void kvm_mmu_put_page(struct kvm_mmu_page *page,
mmu_page_remove_parent_pte(page, parent_pte);
}
static void kvm_mmu_reset_last_pte_updated(struct kvm *kvm)
{
int i;
for (i = 0; i < KVM_MAX_VCPUS; ++i)
if (kvm->vcpus[i])
kvm->vcpus[i]->last_pte_updated = NULL;
}
static void kvm_mmu_zap_page(struct kvm *kvm,
struct kvm_mmu_page *page)
{
@ -717,6 +726,7 @@ static void kvm_mmu_zap_page(struct kvm *kvm,
kvm_mmu_free_page(kvm, page);
} else
list_move(&page->link, &kvm->active_mmu_pages);
kvm_mmu_reset_last_pte_updated(kvm);
}
static int kvm_mmu_unprotect_page(struct kvm_vcpu *vcpu, gfn_t gfn)
@ -1140,6 +1150,13 @@ static void mmu_pte_write_new_pte(struct kvm_vcpu *vcpu,
offset_in_pte);
}
static bool last_updated_pte_accessed(struct kvm_vcpu *vcpu)
{
u64 *spte = vcpu->last_pte_updated;
return !!(spte && (*spte & PT_ACCESSED_MASK));
}
void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
const u8 *new, int bytes)
{
@ -1160,13 +1177,15 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
pgprintk("%s: gpa %llx bytes %d\n", __FUNCTION__, gpa, bytes);
kvm_mmu_audit(vcpu, "pre pte write");
if (gfn == vcpu->last_pt_write_gfn) {
if (gfn == vcpu->last_pt_write_gfn
&& !last_updated_pte_accessed(vcpu)) {
++vcpu->last_pt_write_count;
if (vcpu->last_pt_write_count >= 3)
flooded = 1;
} else {
vcpu->last_pt_write_gfn = gfn;
vcpu->last_pt_write_count = 1;
vcpu->last_pte_updated = NULL;
}
index = kvm_page_table_hashfn(gfn) % KVM_NUM_MMU_PAGES;
bucket = &vcpu->kvm->mmu_page_hash[index];

9
drivers/kvm/paging_tmpl.h
View file

@ -238,7 +238,12 @@ static void FNAME(set_pte_common)(struct kvm_vcpu *vcpu,
FNAME(mark_pagetable_dirty)(vcpu->kvm, walker);
}
spte = PT_PRESENT_MASK | PT_ACCESSED_MASK | PT_DIRTY_MASK;
/*
* We don't set the accessed bit, since we sometimes want to see
* whether the guest actually used the pte (in order to detect
* demand paging).
*/
spte = PT_PRESENT_MASK | PT_DIRTY_MASK;
spte |= gpte & PT64_NX_MASK;
if (!dirty)
access_bits &= ~PT_WRITABLE_MASK;
@ -291,6 +296,8 @@ static void FNAME(set_pte_common)(struct kvm_vcpu *vcpu,
page_header_update_slot(vcpu->kvm, shadow_pte, gaddr);
if (!was_rmapped)
rmap_add(vcpu, shadow_pte);
if (!ptwrite || !*ptwrite)
vcpu->last_pte_updated = shadow_pte;
}
static void FNAME(set_pte)(struct kvm_vcpu *vcpu, pt_element_t gpte,