[patch 3/3] KVM: MMU: prepopulate the shadow on invlpg

Marcelo Tosatti
2008-10-25T22:34:32Z

[-- Attachment #1: invlpg-opt --]
[-- Type: text/plain, Size: 5209 bytes --]

If the guest executes invlpg on a non present entry, peek into th
pagetable and attempt to prepopulate the shadow entry.

Also stop dirty fault updates from interfering with the fork dete

For RHEL3 and 32-bit Vista guests the success rate is high. With Win2003
there is a 1:2 success/fail ratio, but even then compilation benchmarks
are slightly faster. 2000 and XP rarely execute invlpg on non present
entries.

2% improvement on RHEL3/AIM7.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Index: kvm/arch/x86/kvm/mmu.c
===================================================================
--- kvm.orig/arch/x86/kvm/mmu.c
+++ kvm/arch/x86/kvm/mmu.c
@@ -2365,7 +2365,8 @@ static void kvm_mmu_access_page(struct k
}

void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
- const u8 *new, int bytes)
+ const u8 *new, int bytes,
+ bool speculative)
{
gfn_t gfn = gpa >> PAGE_SHIFT;
struct kvm_mmu_page *sp;
@@ -2391,15 +2392,17 @@ void kvm_mmu_pte_write(struct kvm_vcpu *
kvm_mmu_free_some_pages(vcpu);
++vcpu->kvm->stat.mmu_pte_write;
kvm_mmu_audit(vcpu, "pre pte write");
- if (gfn == vcpu->arch.last_pt_write_gfn
- && !last_updated_pte_accessed(vcpu)) {
- ++vcpu->arch.last_pt_write_count;
- if (vcpu->arch.last_pt_write_count >= 3)
- flooded = 1;
- } else {
- vcpu->arch.last_pt_write_gfn = gfn;
- vcpu->arch.last_pt_write_count = 1;
- vcpu->arch.last_pte_updated = NULL;
+ if (!speculative) {
+ if (gfn == vcpu->arch.last_pt_write_gfn
+ && !last_updated_pte_accessed(vcpu)) {
+ ++vcpu->arch.last_pt_write_count;
+ if (vcpu->arch.last_pt_write_count >= 3)
+ flooded = 1;
+ } else {
+ vcpu->arch.last_pt_write_gfn = gfn;
+ vcpu->arch.last_pt_write_count = 1;
+ vcpu->arch.last_pte_updated = NULL;
+ }
}
index = kvm_page_table_hashfn(gfn);
bucket = &vcpu->kvm->arch.mmu_page_hash[index];
@@ -2539,9 +2542,7 @@ EXPORT_SYMBOL_GPL(kvm_mmu_page_fault);

void kvm_mmu_invlpg(struct kvm_vcpu *vcpu, gva_t gva)
{
- spin_lock(&vcpu->kvm->mmu_lock);
vcpu->arch.mmu.invlpg(vcpu, gva);
- spin_unlock(&vcpu->kvm->mmu_lock);
kvm_mmu_flush_tlb(vcpu);
++vcpu->stat.invlpg;
}
Index: kvm/arch/x86/kvm/paging_tmpl.h
===================================================================
--- kvm.orig/arch/x86/kvm/paging_tmpl.h
+++ kvm/arch/x86/kvm/paging_tmpl.h
@@ -82,6 +82,7 @@ struct shadow_walker {
int *ptwrite;
pfn_t pfn;
u64 *sptep;
+ gpa_t pte_gpa;
};

static gfn_t gpte_to_gfn(pt_element_t gpte)
@@ -222,7 +223,7 @@ walk:
if (ret)
goto walk;
pte |= PT_DIRTY_MASK;
- kvm_mmu_pte_write(vcpu, pte_gpa, (u8 *)&pte, sizeof(pte));
+ kvm_mmu_pte_write(vcpu, pte_gpa, (u8 *)&pte, sizeof(pte), 1);
walker->ptes[walker->level - 1] = pte;
}

@@ -467,10 +468,18 @@ static int FNAME(shadow_invlpg_entry)(st
struct kvm_vcpu *vcpu, u64 addr,
u64 *sptep, int level)
{
+ struct shadow_walker *sw =
+ container_of(_sw, struct shadow_walker, walker);

if (level == PT_PAGE_TABLE_LEVEL) {
- if (is_shadow_present_pte(*sptep))
+ struct kvm_mmu_page *sp = page_header(__pa(sptep));
+ sw->pte_gpa = (sp->gfn << PAGE_SHIFT);
+ sw->pte_gpa += (sptep - sp->spt) * sizeof(pt_element_t);
+
+ if (is_shadow_present_pte(*sptep)) {
rmap_remove(vcpu->kvm, sptep);
+ sw->pte_gpa = -1;
+ }
set_shadow_pte(sptep, shadow_trap_nonpresent_pte);
return 1;
}
@@ -481,11 +490,26 @@ static int FNAME(shadow_invlpg_entry)(st

static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva)
{
+ pt_element_t gpte;
struct shadow_walker walker = {
.walker = { .entry = FNAME(shadow_invlpg_entry), },
+ .pte_gpa = -1,
};

+ spin_lock(&vcpu->kvm->mmu_lock);
walk_shadow(&walker.walker, vcpu, gva);
+ spin_unlock(&vcpu->kvm->mmu_lock);
+ if (walker.pte_gpa == -1)
+ return;
+ if (kvm_read_guest_atomic(vcpu->kvm, walker.pte_gpa, &gpte,
+ sizeof(pt_element_t)))
+ return;
+ if (is_present_pte(gpte) && (gpte & PT_ACCESSED_MASK)) {
+ if (mmu_topup_memory_caches(vcpu))
+ return;
+ kvm_mmu_pte_write(vcpu, walker.pte_gpa, (const u8 *)&gpte,
+ sizeof(pt_element_t), 1);
+ }
}

static gpa_t FNAME(gva_to_gpa)(struct kvm_vcpu *vcpu, gva_t vaddr)
Index: kvm/arch/x86/kvm/x86.c
===================================================================
--- kvm.orig/arch/x86/kvm/x86.c
+++ kvm/arch/x86/kvm/x86.c
@@ -2044,7 +2044,7 @@ int emulator_write_phys(struct kvm_vcpu
ret = kvm_write_guest(vcpu->kvm, gpa, val, bytes);
if (ret < 0)
return 0;
- kvm_mmu_pte_write(vcpu, gpa, val, bytes);
+ kvm_mmu_pte_write(vcpu, gpa, val, bytes, 0);
return 1;
}

Index: kvm/include/asm-x86/kvm_host.h
===================================================================
--- kvm.orig/include/asm-x86/kvm_host.h
+++ kvm/include/asm-x86/kvm_host.h
@@ -596,7 +596,8 @@ unsigned long segment_base(u16 selector)

void kvm_mmu_flush_tlb(struct kvm_vcpu *vcpu);
void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
- const u8 *new, int bytes);
+ const u8 *new, int bytes,
+ bool speculative);
int kvm_mmu_unprotect_page_virt(struct kvm_vcpu *vcpu, gva_t gva);
void __kvm_mmu_free_some_pages(struct kvm_vcpu *vcpu);
int kvm_mmu_load(struct kvm_vcpu *vcpu);

--