[PATCH v3 8/9] KVM: VMX: optimize #PF injection when MAXPHYADDR does not match

Mohammed Gamal
2020-07-10T15:49:09Z

From: Paolo Bonzini <pbonzini@redhat.com>

Ignore non-present page faults, since those cannot have reserved
bits set.

When running access.flat with "-cpu Haswell,phys-bits=36", the
number of trapped page faults goes down from 8872644 to 3978948.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/vmx/vmx.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index de3f436b2d32..0cebc4832805 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4355,6 +4355,16 @@ static void init_vmcs(struct vcpu_vmx *vmx)
vmx->pt_desc.guest.output_mask = 0x7F;
vmcs_write64(GUEST_IA32_RTIT_CTL, 0);
}
+
+ /*
+ * If EPT is enabled, #PF is only trapped if MAXPHYADDR is mismatched
+ * between guest and host. In that case we only care about present
+ * faults.
+ */
+ if (enable_ept) {
+ vmcs_write32(PAGE_FAULT_ERROR_CODE_MASK, PFERR_PRESENT_MASK);
+ vmcs_write32(PAGE_FAULT_ERROR_CODE_MATCH, PFERR_PRESENT_MASK);
+ }
}

static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
--
2.26.2