On 11/21/2016 9:07 AM, Paolo Bonzini wrote:
>
>
> 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.
Ah, yes, that is a bit redundant. We'll get rid of the gpa_avail
flag.
Thanks,
Tom
>
>> + }
>>
>> 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)
>>
--
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