On 14/11/2016 23:16, Brijesh Singh wrote:
> From: Tom Lendacky <thomas.lendacky@xxxxxxx>
>
> 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@xxxxxxx>
> Reviewed-by: Borislav Petkov <bp@xxxxxxx>
> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> ---
> arch/x86/include/asm/kvm_emulate.h | 3 +++
> arch/x86/include/asm/kvm_host.h | 3 +++
> arch/x86/kvm/svm.c | 9 ++++++++-
> arch/x86/kvm/x86.c | 17 ++++++++++++++++-
> 4 files changed, 30 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
> index e9cd7be..2d1ac09 100644
> --- a/arch/x86/include/asm/kvm_emulate.h
> +++ b/arch/x86/include/asm/kvm_emulate.h
> @@ -344,6 +344,9 @@ struct x86_emulate_ctxt {
> struct read_cache mem_read;
> };
>
> +/* String operation identifier (matches the definition in emulate.c) */
> +#define CTXT_STRING_OP (1 << 13)
> +
> /* Repeat String Operation Prefix */
> #define REPE_PREFIX 0xf3
> #define REPNE_PREFIX 0xf2
> 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/svm.c b/arch/x86/kvm/svm.c
> index 5e64e656..b442c5a 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -275,6 +275,9 @@ static int avic;
> module_param(avic, int, S_IRUGO);
> #endif
>
> +/* EXITINFO2 contains valid GPA */
> +static bool gpa_avail = true;
> +
> /* AVIC VM ID bit masks and lock */
> static DECLARE_BITMAP(avic_vm_id_bitmap, AVIC_VM_ID_NR);
> static DEFINE_SPINLOCK(avic_vm_id_lock);
> @@ -1055,8 +1058,10 @@ static __init int svm_hardware_setup(void)
> goto err;
> }
>
> - if (!boot_cpu_has(X86_FEATURE_NPT))
> + if (!boot_cpu_has(X86_FEATURE_NPT)) {
> npt_enabled = false;
> + gpa_avail = false;
This is not necessary, since you will never have exit_code ==
SVM_EXIT_NPF && !gpa_avail.
> + }
>
> if (npt_enabled && !npt) {
> printk(KERN_INFO "kvm: Nested Paging disabled\n");
> @@ -4192,6 +4197,8 @@ static int handle_exit(struct kvm_vcpu *vcpu)
> vcpu->arch.cr0 = svm->vmcb->save.cr0;
> if (npt_enabled)
> vcpu->arch.cr3 = svm->vmcb->save.cr3;
> + if (gpa_avail)
> + vcpu->arch.gpa_available = (exit_code == SVM_EXIT_NPF);
The "if", and the body moved just before
return svm_exit_handlers[exit_code](svm);
I'll try doing a similar patch for Intel too, for better testing.
>
> if (unlikely(svm->nested.exit_required)) {
> nested_svm_vmexit(svm);
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d02aeff..c290794 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4420,7 +4420,19 @@ static int vcpu_mmio_gva_to_gpa(struct kvm_vcpu *vcpu, unsigned long gva,
> return 1;
> }
>
> - *gpa = vcpu->arch.walk_mmu->gva_to_gpa(vcpu, gva, access, exception);
> + /*
> + * 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 when the NPF occurred.
> + */
> + if (vcpu->arch.gpa_available &&
> + !(vcpu->arch.emulate_ctxt.d & CTXT_STRING_OP))
> + *gpa = exception->address;
> + else
> + *gpa = vcpu->arch.walk_mmu->gva_to_gpa(vcpu, gva, access,
> + exception);
>
> if (*gpa == UNMAPPED_GVA)
> return -1;
> @@ -5542,6 +5554,9 @@ 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)
>
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
