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

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Message-Id: <20200710154811.418214-9-mgamal@redhat.com>
Date:   Fri, 10 Jul 2020 17:48:10 +0200
From:   Mohammed Gamal <mgamal@...hat.com>
To:     kvm@...r.kernel.org, pbonzini@...hat.com
Cc:     linux-kernel@...r.kernel.org, vkuznets@...hat.com,
        sean.j.christopherson@...el.com, wanpengli@...cent.com,
        jmattson@...gle.com, joro@...tes.org
Subject: [PATCH v3 8/9] KVM: VMX: optimize #PF injection when MAXPHYADDR does not match

From: Paolo Bonzini <pbonzini@...hat.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@...hat.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