[PATCH 2/3] KVM: x86: Avoid guest page table walk when gpa_available is set

[Paolo Bonzini]

From: Brijesh Singh <brijesh.singh@xxxxxxx>

When a guest causes a page fault which requires emulation, the
vcpu->arch.gpa_available flag is set to indicate that cr2 contains a
valid GPA.

Currently, emulator_read_write_onepage() makes use of gpa_available flag
to avoid a guest page walk for a known MMIO regions. Lets not limit
the gpa_available optimization to just MMIO region. The patch extends
the check to avoid page walk whenever gpa_available flag is set.

Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
[Fix EPT=0 according to Wanpeng Li's fix, plus ensure VMX also uses the
 new code. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h |  3 ++-
 arch/x86/kvm/mmu.c              |  9 +++++++++
 arch/x86/kvm/svm.c              |  3 +--
 arch/x86/kvm/vmx.c              |  3 ---
 arch/x86/kvm/x86.c              | 19 ++++++-------------
 5 files changed, 18 insertions(+), 19 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 9e4862e0e978..6db0ed9cf59e 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -685,8 +685,9 @@ struct kvm_vcpu_arch {
 	int pending_ioapic_eoi;
 	int pending_external_vector;
 
-	/* GPA available (AMD only) */
+	/* GPA available */
 	bool gpa_available;
+	gpa_t gpa_val;
 
 	/* be preempted when it's in kernel-mode(cpl=0) */
 	bool preempted_in_kernel;
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 5339d83916bf..f5c3f8e7d29f 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4829,6 +4829,15 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u64 error_code,
 	enum emulation_result er;
 	bool direct = vcpu->arch.mmu.direct_map || mmu_is_nested(vcpu);
 
+	/*
+	 * With shadow page tables, fault_address contains a GVA
+	 * or nested GPA.
+	 */
+	if (vcpu->arch.mmu.direct_map) {
+		vcpu->arch.gpa_available = true;
+		vcpu->arch.gpa_val = cr2;
+	}
+
 	if (unlikely(error_code & PFERR_RSVD_MASK)) {
 		r = handle_mmio_page_fault(vcpu, cr2, direct);
 		if (r == RET_MMIO_PF_EMULATE) {
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 1fa9ee5660f4..c5c6b182cddf 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -4235,8 +4235,7 @@ static int handle_exit(struct kvm_vcpu *vcpu)
 	u32 exit_code = svm->vmcb->control.exit_code;
 
 	trace_kvm_exit(exit_code, vcpu, KVM_ISA_SVM);
-
-	vcpu->arch.gpa_available = (exit_code == SVM_EXIT_NPF);
+	vcpu->arch.gpa_available = false;
 
 	if (!is_cr_intercept(svm, INTERCEPT_CR0_WRITE))
 		vcpu->arch.cr0 = svm->vmcb->save.cr0;
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 45fb0ea78ee8..79efb00dd70d 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -6393,9 +6393,7 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
 	error_code |= (exit_qualification & 0x100) != 0 ?
 	       PFERR_GUEST_FINAL_MASK : PFERR_GUEST_PAGE_MASK;
 
-	vcpu->arch.gpa_available = true;
 	vcpu->arch.exit_qualification = exit_qualification;
-
 	return kvm_mmu_page_fault(vcpu, gpa, error_code, NULL, 0);
 }
 
@@ -6410,7 +6408,6 @@ static int handle_ept_misconfig(struct kvm_vcpu *vcpu)
 		return kvm_skip_emulated_instruction(vcpu);
 	}
 
-	vcpu->arch.gpa_available = true;
 	ret = kvm_mmu_page_fault(vcpu, gpa, PFERR_RSVD_MASK, NULL, 0);
 	if (ret >= 0)
 		return ret;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e40a779711a9..bb05b705c295 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4657,25 +4657,18 @@ static int emulator_read_write_onepage(unsigned long addr, void *val,
 	 */
 	if (vcpu->arch.gpa_available &&
 	    emulator_can_use_gpa(ctxt) &&
-	    vcpu_is_mmio_gpa(vcpu, addr, exception->address, write) &&
-	    (addr & ~PAGE_MASK) == (exception->address & ~PAGE_MASK)) {
-		gpa = exception->address;
-		goto mmio;
+	    (addr & ~PAGE_MASK) == (vcpu->arch.gpa_val & ~PAGE_MASK)) {
+		gpa = vcpu->arch.gpa_val;
+		ret = vcpu_is_mmio_gpa(vcpu, addr, gpa, write);
+	} else {
+		ret = vcpu_mmio_gva_to_gpa(vcpu, addr, &gpa, exception, write);
 	}
 
-	ret = vcpu_mmio_gva_to_gpa(vcpu, addr, &gpa, exception, write);
-
 	if (ret < 0)
 		return X86EMUL_PROPAGATE_FAULT;
-
-	/* For APIC access vmexit */
-	if (ret)
-		goto mmio;
-
-	if (ops->read_write_emulate(vcpu, gpa, val, bytes))
+	if (!ret && ops->read_write_emulate(vcpu, gpa, val, bytes))
 		return X86EMUL_CONTINUE;
 
-mmio:
 	/*
 	 * Is this MMIO handled locally?
 	 */
-- 
1.8.3.1