[PATCH v2 01/26] KVM: x86/mmu: Optimize MMU page cache lookup for all direct SPs

David Matlack
2022-03-11T00:25:36Z

Commit fb58a9c345f6 ("KVM: x86/mmu: Optimize MMU page cache lookup for
fully direct MMUs") skipped the unsync checks and write flood clearing
for full direct MMUs. We can extend this further and skip the checks for
all direct shadow pages. Direct shadow pages are never marked unsynced
or have a non-zero write-flooding count.

Checking sp->role.direct alos generates better code than checking
direct_map because, due to register pressure, direct_map has to get
shoved onto the stack and then pulled back off.

No functional change intended.

Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
---
arch/x86/kvm/mmu/mmu.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 3b8da8b0745e..3ad67f70e51c 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2034,7 +2034,6 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
int direct,
unsigned int access)
{
- bool direct_mmu = vcpu->arch.mmu->direct_map;
union kvm_mmu_page_role role;
struct hlist_head *sp_list;
unsigned quadrant;
@@ -2075,7 +2074,8 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu,
continue;
}

- if (direct_mmu)
+ /* unsync and write-flooding only apply to indirect SPs. */
+ if (sp->role.direct)
goto trace_get_page;

if (sp->unsync) {

base-commit: ce41d078aaa9cf15cbbb4a42878cc6160d76525e
--
2.35.1.723.g4982287a31-goog