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KVM: MMU: improve write flooding detected

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Detecting write-flooding does not work well, when we handle page written, if
the last speculative spte is not accessed, we treat the page is
write-flooding, however, we can speculative spte on many path, such as pte
prefetch, page synced, that means the last speculative spte may be not point
to the written page and the written page can be accessed via other sptes, so
depends on the Accessed bit of the last speculative spte is not enough

Instead of detected page accessed, we can detect whether the spte is accessed
after it is written, if the spte is not accessed but it is written frequently,
we treat is not a page table or it not used for a long time

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Xiao Guangrong
2011-09-22 16:58:36 +08:00
committed by Avi Kivity
parent 5d9ca30e96
commit a30f47cb15
3 changed files with 32 additions and 48 deletions
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12
arch/x86/kvm/paging_tmpl.h
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@@ -497,6 +497,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
shadow_walk_next(&it)) {
gfn_t table_gfn;
clear_sp_write_flooding_count(it.sptep);
drop_large_spte(vcpu, it.sptep);
sp = NULL;
@@ -522,6 +523,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
shadow_walk_next(&it)) {
gfn_t direct_gfn;
clear_sp_write_flooding_count(it.sptep);
validate_direct_spte(vcpu, it.sptep, direct_access);
drop_large_spte(vcpu, it.sptep);
@@ -536,6 +538,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
link_shadow_page(it.sptep, sp);
}
clear_sp_write_flooding_count(it.sptep);
mmu_set_spte(vcpu, it.sptep, access, gw->pte_access,
user_fault, write_fault, emulate, it.level,
gw->gfn, pfn, prefault, map_writable);
@@ -599,11 +602,9 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
*/
if (!r) {
pgprintk("%s: guest page fault\n", __func__);
if (!prefault) {
if (!prefault)
inject_page_fault(vcpu, &walker.fault);
/* reset fork detector */
vcpu->arch.last_pt_write_count = 0;
}
return 0;
}
@@ -641,9 +642,6 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
pgprintk("%s: shadow pte %p %llx emulate %d\n", __func__,
sptep, *sptep, emulate);
if (!emulate)
vcpu->arch.last_pt_write_count = 0; /* reset fork detector */
++vcpu->stat.pf_fixed;
trace_kvm_mmu_audit(vcpu, AUDIT_POST_PAGE_FAULT);
spin_unlock(&vcpu->kvm->mmu_lock);