[PATCH 5/5] KVM: x86: MMU: Eliminate an extra memory slot search in mapping_level()

Takuya Yoshikawa
2015-10-16T07:55:08Z

Calling kvm_vcpu_gfn_to_memslot() twice in mapping_level() should be
avoided since getting a slot by binary search may not be negligible,
especially for virtual machines with many memory slots.

Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
---
arch/x86/kvm/mmu.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 09833b0..dd2a7c6 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -818,14 +818,11 @@ static void unaccount_shadowed(struct kvm *kvm, struct kvm_mmu_page *sp)
kvm->arch.indirect_shadow_pages--;
}

-static int has_wrprotected_page(struct kvm_vcpu *vcpu,
- gfn_t gfn,
- int level)
+static int __has_wrprotected_page(gfn_t gfn, int level,
+ struct kvm_memory_slot *slot)
{
- struct kvm_memory_slot *slot;
struct kvm_lpage_info *linfo;

- slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
if (slot) {
linfo = lpage_info_slot(gfn, slot, level);
return linfo->write_count;
@@ -834,6 +831,14 @@ static int has_wrprotected_page(struct kvm_vcpu *vcpu,
return 1;
}

+static int has_wrprotected_page(struct kvm_vcpu *vcpu, gfn_t gfn, int level)
+{
+ struct kvm_memory_slot *slot;
+
+ slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
+ return __has_wrprotected_page(gfn, level, slot);
+}
+
static int host_mapping_level(struct kvm *kvm, gfn_t gfn)
{
unsigned long page_size;
@@ -896,7 +901,7 @@ static int mapping_level(struct kvm_vcpu *vcpu, gfn_t large_gfn,
max_level = min(kvm_x86_ops->get_lpage_level(), host_level);

for (level = PT_DIRECTORY_LEVEL; level <= max_level; ++level)
- if (has_wrprotected_page(vcpu, large_gfn, level))
+ if (__has_wrprotected_page(large_gfn, level, slot))
break;

return level - 1;
--
2.1.0