Commit 618232e2 authored by Brijesh Singh's avatar Brijesh Singh Committed by Radim Krčmář
Browse files

KVM: x86: Avoid guest page table walk when gpa_available is set 



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: default avatarBrijesh Singh <brijesh.singh@amd.com>
[Fix EPT=0 according to Wanpeng Li's fix, plus ensure VMX also uses the
 new code. - Paolo]
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
[Moved "ret < 0" to the else brach, as per David's review. - Radim]
Signed-off-by: default avatarRadim Krčmář <rkrcmar@redhat.com>
parent e08d26f0

arch/x86/include/asm/kvm_host.h

+2 −1
Original line number Diff line number Diff line
@@ -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;

arch/x86/kvm/mmu.c

+6 −0
Original line number Diff line number Diff line
@@ -4843,6 +4843,12 @@ 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 nGPA.  */

	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) {

arch/x86/kvm/svm.c

+0 −2
Original line number Diff line number Diff line
@@ -4236,8 +4236,6 @@ static int handle_exit(struct kvm_vcpu *vcpu) 


	trace_kvm_exit(exit_code, vcpu, KVM_ISA_SVM);



	vcpu->arch.gpa_available = (exit_code == SVM_EXIT_NPF);



	if (!is_cr_intercept(svm, INTERCEPT_CR0_WRITE))

		vcpu->arch.cr0 = svm->vmcb->save.cr0;

	if (npt_enabled)

arch/x86/kvm/vmx.c

+0 −4
Original line number Diff line number Diff line
@@ -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;
@@ -8644,7 +8641,6 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu) 
	u32 vectoring_info = vmx->idt_vectoring_info;



	trace_kvm_exit(exit_reason, vcpu, KVM_ISA_VMX);

	vcpu->arch.gpa_available = false;



	/*

	 * Flush logged GPAs PML buffer, this will make dirty_bitmap more

arch/x86/kvm/x86.c

+9 −15
Original line number Diff line number Diff line
@@ -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);



		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?

	 */
@@ -7002,6 +6995,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) 
	if (vcpu->arch.apic_attention)

		kvm_lapic_sync_from_vapic(vcpu);



	vcpu->arch.gpa_available = false;

	r = kvm_x86_ops->handle_exit(vcpu);

	return r;

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