From: Brijesh Singh <brijesh.singh@amd.com>
To: <pbonzini@redhat.com>, <rkrcmar@redhat.com>, <joro@8bytes.org>,
<kvm@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Cc: <brijesh.singh@amd.com>, <tglx@linutronix.de>, <mingo@redhat.com>,
<hpa@zytor.com>, <x86@kernel.org>, <Thomas.Lendacky@amd.com>
Subject: Re: [PATCH] x86: kvm: Avoid guest page table walk when gpa_available is set
Date: Mon, 24 Apr 2017 11:16:05 -0500 [thread overview]
Message-ID: <407864ef-c815-6e94-a8c3-0307821d513a@amd.com> (raw)
In-Reply-To: <1493049146-19261-1-git-send-email-brijesh.singh@amd.com>
On 04/24/2017 10:52 AM, Brijesh Singh wrote:
> On AMD hardware when a guest causes a NFP which requires emulation,
Just realized a typo in patch description, s/NFP/NPF
> 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@amd.com>
> ---
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/svm.c | 4 ++++
> arch/x86/kvm/x86.c | 26 +++++++++++++++-----------
> 3 files changed, 20 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 74ef58c..491326d 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -677,6 +677,7 @@ struct kvm_vcpu_arch {
>
> /* GPA available (AMD only) */
> bool gpa_available;
> + gpa_t gpa_val;
> };
>
> struct kvm_lpage_info {
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 5fba706..8827e4b 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -4159,6 +4159,10 @@ static int handle_exit(struct kvm_vcpu *vcpu)
>
> vcpu->arch.gpa_available = (exit_code == SVM_EXIT_NPF);
>
> + /* On #NPF, exit_info_2 contain a valid GPA */
> + if (vcpu->arch.gpa_available)
> + vcpu->arch.gpa_val = svm->vmcb->control.exit_info_2;
> +
> if (!is_cr_intercept(svm, INTERCEPT_CR0_WRITE))
> vcpu->arch.cr0 = svm->vmcb->save.cr0;
> if (npt_enabled)
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index ccbd45e..18ec746 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4653,18 +4653,16 @@ static int emulator_read_write_onepage(unsigned long addr, void *val,
> * occurred.
> */
> 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)) {
> + emulator_can_use_gpa(ctxt) &&
> + (addr & ~PAGE_MASK) == (exception->address & ~PAGE_MASK)) {
> gpa = exception->address;
> - goto mmio;
> + 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;
> }
>
> - 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;
> @@ -5675,8 +5673,14 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
> }
>
> restart:
> - /* Save the faulting GPA (cr2) in the address field */
> - ctxt->exception.address = cr2;
> + /*
> + * Save the faulting GPA (cr2) in the address field
> + * NOTE: If gpa_available is set then gpa_val will contain a valid GPA
> + */
> + if (vcpu->arch.gpa_available)
> + ctxt->exception.address = vcpu->arch.gpa_val;
> + else
> + ctxt->exception.address = cr2;
>
> r = x86_emulate_insn(ctxt);
>
>
next prev parent reply other threads:[~2017-04-24 16:16 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-24 15:52 [PATCH] x86: kvm: Avoid guest page table walk when gpa_available is set Brijesh Singh
2017-04-24 16:16 ` Brijesh Singh [this message]
2017-04-24 20:52 ` Radim Krčmář
2017-04-24 22:14 ` Brijesh Singh
2017-04-25 14:03 ` Radim Krčmář
2017-04-25 22:02 ` Brijesh Singh
2017-04-26 20:44 ` Radim Krčmář
2017-04-28 19:15 ` Brijesh Singh
2017-05-02 16:24 ` Paolo Bonzini
2017-05-02 21:44 ` Brijesh Singh
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