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KVM: MMU: Avoid unnecessary remote tlb flushes when guest updates a pte

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If all we're doing is increasing permissions on a pte (typical for demand
paging), then there's not need to flush remote tlbs.  Worst case they'll
get a spurious page fault.

Signed-off-by: Avi Kivity <avi@qumranet.com>
This commit is contained in:
Avi Kivity 2007-11-21 02:06:21 +02:00
parent 0f74a24c59
commit 79539cec0c
1 changed files with 26 additions and 1 deletions
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27
drivers/kvm/mmu.c
View file

@ -134,6 +134,8 @@ static int dbg = 1;
#define PT32_DIR_BASE_ADDR_MASK \ #define PT32_DIR_BASE_ADDR_MASK \
(PAGE_MASK & ~((1ULL << (PAGE_SHIFT + PT32_LEVEL_BITS)) - 1)) (PAGE_MASK & ~((1ULL << (PAGE_SHIFT + PT32_LEVEL_BITS)) - 1))
#define PT64_PERM_MASK (PT_PRESENT_MASK | PT_WRITABLE_MASK | PT_USER_MASK \
| PT64_NX_MASK)
#define PFERR_PRESENT_MASK (1U << 0) #define PFERR_PRESENT_MASK (1U << 0)
#define PFERR_WRITE_MASK (1U << 1) #define PFERR_WRITE_MASK (1U << 1)
@ -1227,7 +1229,6 @@ static void mmu_pte_write_zap_pte(struct kvm_vcpu *vcpu,
} }
} }
set_shadow_pte(spte, shadow_trap_nonpresent_pte); set_shadow_pte(spte, shadow_trap_nonpresent_pte);
kvm_flush_remote_tlbs(vcpu->kvm);
} }
static void mmu_pte_write_new_pte(struct kvm_vcpu *vcpu, static void mmu_pte_write_new_pte(struct kvm_vcpu *vcpu,
@ -1250,6 +1251,27 @@ static void mmu_pte_write_new_pte(struct kvm_vcpu *vcpu,
offset_in_pte); offset_in_pte);
} }
static bool need_remote_flush(u64 old, u64 new)
{
if (!is_shadow_present_pte(old))
return false;
if (!is_shadow_present_pte(new))
return true;
if ((old ^ new) & PT64_BASE_ADDR_MASK)
return true;
old ^= PT64_NX_MASK;
new ^= PT64_NX_MASK;
return (old & ~new & PT64_PERM_MASK) != 0;
}
static void mmu_pte_write_flush_tlb(struct kvm_vcpu *vcpu, u64 old, u64 new)
{
if (need_remote_flush(old, new))
kvm_flush_remote_tlbs(vcpu->kvm);
else
kvm_mmu_flush_tlb(vcpu);
}
static bool last_updated_pte_accessed(struct kvm_vcpu *vcpu) static bool last_updated_pte_accessed(struct kvm_vcpu *vcpu)
{ {
u64 *spte = vcpu->last_pte_updated; u64 *spte = vcpu->last_pte_updated;
@ -1265,6 +1287,7 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
struct hlist_node *node, *n; struct hlist_node *node, *n;
struct hlist_head *bucket; struct hlist_head *bucket;
unsigned index; unsigned index;
u64 entry;
u64 *spte; u64 *spte;
unsigned offset = offset_in_page(gpa); unsigned offset = offset_in_page(gpa);
unsigned pte_size; unsigned pte_size;
@ -1335,9 +1358,11 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
} }
spte = &page->spt[page_offset / sizeof(*spte)]; spte = &page->spt[page_offset / sizeof(*spte)];
while (npte--) { while (npte--) {
entry = *spte;
mmu_pte_write_zap_pte(vcpu, page, spte); mmu_pte_write_zap_pte(vcpu, page, spte);
mmu_pte_write_new_pte(vcpu, page, spte, new, bytes, mmu_pte_write_new_pte(vcpu, page, spte, new, bytes,
page_offset & (pte_size - 1)); page_offset & (pte_size - 1));
mmu_pte_write_flush_tlb(vcpu, entry, *spte);
++spte; ++spte;
} }
} }