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Message-ID: <416da478-824b-7a68-2fc8-17a29550b119@redhat.com>
Date: Tue, 29 Nov 2016 19:10:14 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Brijesh Singh <brijesh.singh@....com>, kvm@...r.kernel.org
Cc: thomas.lendacky@....com, rkrcmar@...hat.com, joro@...tes.org,
x86@...nel.org, linux-kernel@...r.kernel.org, mingo@...hat.com,
hpa@...or.com, tglx@...utronix.de, bp@...e.de
Subject: Re: [PATCH v3] kvm: svm: Use the hardware provided GPA instead of
page walk
On 29/11/2016 19:01, Brijesh Singh wrote:
> From: Tom Lendacky <thomas.lendacky@....com>
>
> When a guest causes a NPF which requires emulation, KVM sometimes walks
> the guest page tables to translate the GVA to a GPA. This is unnecessary
> most of the time on AMD hardware since the hardware provides the GPA in
> EXITINFO2.
>
> The only exception cases involve string operations involving rep or
> operations that use two memory locations. With rep, the GPA will only be
> the value of the initial NPF and with dual memory locations we won't know
> which memory address was translated into EXITINFO2.
>
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> Reviewed-by: Borislav Petkov <bp@...e.de>
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> ---
> arch/x86/include/asm/kvm_emulate.h | 1 +
> arch/x86/include/asm/kvm_host.h | 3 ++
> arch/x86/kvm/emulate.c | 8 +++++++
> arch/x86/kvm/svm.c | 2 ++
> arch/x86/kvm/x86.c | 44 ++++++++++++++++++++++++++++--------
> 5 files changed, 48 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
> index e9cd7be..777eea2 100644
> --- a/arch/x86/include/asm/kvm_emulate.h
> +++ b/arch/x86/include/asm/kvm_emulate.h
> @@ -441,5 +441,6 @@ int emulator_task_switch(struct x86_emulate_ctxt *ctxt,
> int emulate_int_real(struct x86_emulate_ctxt *ctxt, int irq);
> void emulator_invalidate_register_cache(struct x86_emulate_ctxt *ctxt);
> void emulator_writeback_register_cache(struct x86_emulate_ctxt *ctxt);
> +bool emulator_is_string_op(struct x86_emulate_ctxt *ctxt);
>
> #endif /* _ASM_X86_KVM_X86_EMULATE_H */
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 77cb3f9..fd5b1c8 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -668,6 +668,9 @@ struct kvm_vcpu_arch {
>
> int pending_ioapic_eoi;
> int pending_external_vector;
> +
> + /* GPA available (AMD only) */
> + bool gpa_available;
> };
>
> struct kvm_lpage_info {
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index a3ce9d2..0ea543e 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -5483,3 +5483,11 @@ void emulator_writeback_register_cache(struct x86_emulate_ctxt *ctxt)
> {
> writeback_registers(ctxt);
> }
> +
> +bool emulator_is_string_op(struct x86_emulate_ctxt *ctxt)
> +{
> + if (ctxt->d & String)
> + return true;
> +
> + return false;
> +}
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 5e64e656..e9b3555 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -4188,6 +4188,8 @@ 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)
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c30f62dc..507c75c 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4420,6 +4420,21 @@ int kvm_write_guest_virt_system(struct x86_emulate_ctxt *ctxt,
> }
> EXPORT_SYMBOL_GPL(kvm_write_guest_virt_system);
>
> +static int vcpu_is_mmio_gpa(struct kvm_vcpu *vcpu, unsigned long gva,
> + gpa_t gpa, bool write)
> +{
> + /* For APIC access vmexit */
> + if ((gpa & PAGE_MASK) == APIC_DEFAULT_PHYS_BASE)
> + return 1;
> +
> + if (vcpu_match_mmio_gpa(vcpu, gpa)) {
> + trace_vcpu_match_mmio(gva, gpa, write, true);
> + return 1;
> + }
> +
> + return 0;
> +}
> +
> static int vcpu_mmio_gva_to_gpa(struct kvm_vcpu *vcpu, unsigned long gva,
> gpa_t *gpa, struct x86_exception *exception,
> bool write)
> @@ -4446,16 +4461,7 @@ static int vcpu_mmio_gva_to_gpa(struct kvm_vcpu *vcpu, unsigned long gva,
> if (*gpa == UNMAPPED_GVA)
> return -1;
>
> - /* For APIC access vmexit */
> - if ((*gpa & PAGE_MASK) == APIC_DEFAULT_PHYS_BASE)
> - return 1;
> -
> - if (vcpu_match_mmio_gpa(vcpu, *gpa)) {
> - trace_vcpu_match_mmio(gva, *gpa, write, true);
> - return 1;
> - }
> -
> - return 0;
> + return vcpu_is_mmio_gpa(vcpu, gva, *gpa, write);
> }
>
> int emulator_write_phys(struct kvm_vcpu *vcpu, gpa_t gpa,
> @@ -4552,6 +4558,21 @@ static int emulator_read_write_onepage(unsigned long addr, void *val,
> int handled, ret;
> bool write = ops->write;
> struct kvm_mmio_fragment *frag;
> + struct x86_emulate_ctxt *ctxt = &vcpu->arch.emulate_ctxt;
> +
> + /*
> + * If the exit was due to a NPF we may already have a GPA.
> + * If the GPA is present, use it to avoid the GVA to GPA table walk.
> + * Note, this cannot be used on string operations since string
> + * operation using rep will only have the initial GPA from the NPF
> + * occurred.
> + */
> + if (vcpu->arch.gpa_available &&
> + !emulator_is_string_op(ctxt) &&
> + vcpu_is_mmio_gpa(vcpu, addr, exception->address, write)) {
> + gpa = exception->address;
> + goto mmio;
> + }
>
> ret = vcpu_mmio_gva_to_gpa(vcpu, addr, &gpa, exception, write);
>
> @@ -5563,6 +5584,9 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
> }
>
> restart:
> + /* Save the faulting GPA (cr2) in the address field */
> + ctxt->exception.address = cr2;
> +
> r = x86_emulate_insn(ctxt);
>
> if (r == EMULATION_INTERCEPTED)
>
Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
Thanks!
Paolo
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