linux-kernel - Re: [PATCH v4 01/12] KVM: x86/mmu: helpers to return if KVM honors guest MTRRs

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Message-ID: <ZSRZ_y64UPXBG6lA@google.com>
Date:   Mon, 9 Oct 2023 12:52:31 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Like Xu <like.xu.linux@...il.com>
Cc:     Yan Zhao <yan.y.zhao@...el.com>, pbonzini@...hat.com,
        chao.gao@...el.com, kai.huang@...el.com,
        robert.hoo.linux@...il.com, yuan.yao@...ux.intel.com,
        kvm list <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 01/12] KVM: x86/mmu: helpers to return if KVM honors
 guest MTRRs

On Sat, Oct 07, 2023, Like Xu wrote:
> On 14/7/2023 2:50 pm, Yan Zhao wrote:
> > Added helpers to check if KVM honors guest MTRRs.
> > The inner helper __kvm_mmu_honors_guest_mtrrs() is also provided to
> > outside callers for the purpose of checking if guest MTRRs were honored
> > before stopping non-coherent DMA.
> > 
> > Suggested-by: Sean Christopherson <seanjc@...gle.com>
> > Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
> > ---
> >   arch/x86/kvm/mmu.h     |  7 +++++++
> >   arch/x86/kvm/mmu/mmu.c | 15 +++++++++++++++
> >   2 files changed, 22 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> > index 92d5a1924fc1..38bd449226f6 100644
> > --- a/arch/x86/kvm/mmu.h
> > +++ b/arch/x86/kvm/mmu.h
> > @@ -235,6 +235,13 @@ static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
> >   	return -(u32)fault & errcode;
> >   }
> > +bool __kvm_mmu_honors_guest_mtrrs(struct kvm *kvm, bool vm_has_noncoherent_dma);
> > +
> > +static inline bool kvm_mmu_honors_guest_mtrrs(struct kvm *kvm)
> > +{
> > +	return __kvm_mmu_honors_guest_mtrrs(kvm, kvm_arch_has_noncoherent_dma(kvm));
> > +}
> > +
> >   void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end);
> >   int kvm_arch_write_log_dirty(struct kvm_vcpu *vcpu);
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 1e5db621241f..b4f89f015c37 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -4516,6 +4516,21 @@ static int kvm_tdp_mmu_page_fault(struct kvm_vcpu *vcpu,
> >   }
> >   #endif
> > +bool __kvm_mmu_honors_guest_mtrrs(struct kvm *kvm, bool vm_has_noncoherent_dma)
> 
> According to the motivation provided in the comment, the function will no
> longer need to be passed the parameter "struct kvm *kvm" but will rely on
> the global parameters (plus vm_has_noncoherent_dma), removing "*kvm" ?

Yeah, I'll fixup the commit to drop @kvm from the inner helper.  Thanks!