Messages in this thread | | | Date | Sat, 19 Feb 2022 11:03:49 +0100 | Subject | Re: [PATCH v2 14/18] KVM: x86/mmu: avoid indirect call for get_cr3 | From | Paolo Bonzini <> |
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On 2/18/22 21:30, Sean Christopherson wrote: > On Thu, Feb 17, 2022, Paolo Bonzini wrote: >> Most of the time, calls to get_guest_pgd result in calling >> kvm_read_cr3 (the exception is only nested TDP). Hardcode >> the default instead of using the get_cr3 function, avoiding >> a retpoline if they are enabled. >> >> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> >> --- >> arch/x86/kvm/mmu.h | 13 +++++++++++++ >> arch/x86/kvm/mmu/mmu.c | 15 +++++---------- >> arch/x86/kvm/mmu/paging_tmpl.h | 2 +- >> arch/x86/kvm/x86.c | 2 +- >> 4 files changed, 20 insertions(+), 12 deletions(-) >> >> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h >> index 1d0c1904d69a..1808d6814ddb 100644 >> --- a/arch/x86/kvm/mmu.h >> +++ b/arch/x86/kvm/mmu.h >> @@ -116,6 +116,19 @@ static inline void kvm_mmu_load_pgd(struct kvm_vcpu *vcpu) >> vcpu->arch.mmu->shadow_root_level); >> } >> >> +static inline gpa_t __kvm_mmu_get_guest_pgd(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu) >> +{ > > I'd prefer to do what we do for page faults. That approach avoids the need for a > comment to document NULL and avoids a conditional when RETPOLINE is not enabled. > > Might be worth renaming get_cr3 => get_guest_cr3 though.
I did it this way to avoid a slightly gratuitous extern function just because kvm_mmu_get_guest_pgd and kvm_read_cr3 are both inline. But at least it's not an export since there are no callers in vmx/svm, so it's okay to do it as you suggested.
> #ifdef CONFIG_RETPOLINE > if (mmu->get_guest_pgd = get_guest_cr3) > return kvm_read_cr3(vcpu); > #endif > return mmu->get_guest_pgd(vcpu); > > >> + if (!mmu->get_guest_pgd) >> + return kvm_read_cr3(vcpu); >> + else >> + return mmu->get_guest_pgd(vcpu); >> +} >> + >> +static inline gpa_t kvm_mmu_get_guest_pgd(struct kvm_vcpu *vcpu) >> +{ >> + return __kvm_mmu_get_guest_pgd(vcpu, vcpu->arch.mmu); > > I'd much prefer we don't provide an @vcpu-only variant and force the caller to > provide the mmu.
No problem.
Paolo
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