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Mon, 09 Oct 2023 14:27:17 -0700 (PDT) Date: Mon, 9 Oct 2023 14:27:16 -0700 In-Reply-To: Mime-Version: 1.0 References: <20230714064656.20147-1-yan.y.zhao@intel.com> <20230714065006.20201-1-yan.y.zhao@intel.com> <553e3a0f-156b-e5d2-037b-2d9acaf52329@gmail.com> Message-ID: Subject: Re: [PATCH v4 01/12] KVM: x86/mmu: helpers to return if KVM honors guest MTRRs From: Sean Christopherson To: Like Xu Cc: Yan Zhao , pbonzini@redhat.com, chao.gao@intel.com, kai.huang@intel.com, robert.hoo.linux@gmail.com, yuan.yao@linux.intel.com, kvm list , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Oct 09, 2023, Sean Christopherson wrote: > On Sat, Oct 07, 2023, Like Xu wrote: > > On 14/7/2023 2:50=E2=80=AFpm, Yan Zhao wrote: > > > 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_vcp= u *vcpu, struct kvm_mmu *mmu, > > > return -(u32)fault & errcode; > > > } > > > +bool __kvm_mmu_honors_guest_mtrrs(struct kvm *kvm, bool vm_has_nonco= herent_dma); > > > + > > > +static inline bool kvm_mmu_honors_guest_mtrrs(struct kvm *kvm) > > > +{ > > > + return __kvm_mmu_honors_guest_mtrrs(kvm, kvm_arch_has_noncoherent_d= ma(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_v= cpu *vcpu, > > > } > > > #endif > > > +bool __kvm_mmu_honors_guest_mtrrs(struct kvm *kvm, bool vm_has_nonco= herent_dma) > >=20 > > 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" ? >=20 > Yeah, I'll fixup the commit to drop @kvm from the inner helper. Thanks! Gah, and I gave more bad advice when I suggested this idea. There's no nee= d to explicitly check tdp_enabled, as shadow_memtype_mask is set to zero if TDP = is disabled. And that must be the case, e.g. make_spte() would generate a cor= rupt shadow_memtype_mask were non-zero on Intel with shadow paging. Yan, can you take a look at what I ended up with (see below) to make sure i= t looks sane/acceptable to you? New hashes (assuming I didn't botch things and need even more fixup). [1/5] KVM: x86/mmu: Add helpers to return if KVM honors guest MTRRs https://github.com/kvm-x86/linux/commit/ec1d8217d59b [2/5] KVM: x86/mmu: Zap SPTEs when CR0.CD is toggled iff guest MTRRs are ho= nored https://github.com/kvm-x86/linux/commit/40de16c10b9d [3/5] KVM: x86/mmu: Zap SPTEs on MTRR update iff guest MTRRs are honored https://github.com/kvm-x86/linux/commit/defc3fae8d0f [4/5] KVM: x86/mmu: Zap KVM TDP when noncoherent DMA assignment starts/stop= s https://github.com/kvm-x86/linux/commit/b344d331adeb [5/5] KVM: VMX: drop IPAT in memtype when CD=3D1 for KVM_X86_QUIRK_CD_NW_CL= EARED https://github.com/kvm-x86/linux/commit/a4d14445c47d commit ec1d8217d59bd7cb03ae4e80551fee987be98a4e Author: Yan Zhao Date: Fri Jul 14 14:50:06 2023 +0800 KVM: x86/mmu: Add helpers to return if KVM honors guest MTRRs =20 Add helpers to check if KVM honors guest MTRRs instead of open coding t= he logic in kvm_tdp_page_fault(). Future fixes and cleanups will also nee= d to determine if KVM should honor guest MTRRs, e.g. for CR0.CD toggling = and and non-coherent DMA transitions. =20 Provide an inner helper, __kvm_mmu_honors_guest_mtrrs(), so that KVM ca= n if guest MTRRs were honored when stopping non-coherent DMA. =20 Note, there is no need to explicitly check that TDP is enabled, KVM cle= ars shadow_memtype_mask when TDP is disabled, i.e. it's non-zero if and onl= y if EPT is enabled. =20 Suggested-by: Sean Christopherson Signed-off-by: Yan Zhao Link: https://lore.kernel.org/r/20230714065006.20201-1-yan.y.zhao@intel= .com Link: https://lore.kernel.org/r/20230714065043.20258-1-yan.y.zhao@intel= .com [sean: squash into a one patch, drop explicit TDP check massage changel= og] Signed-off-by: Sean Christopherson diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h index 253fb2093d5d..bb8c86eefac0 100644 --- a/arch/x86/kvm/mmu.h +++ b/arch/x86/kvm/mmu.h @@ -237,6 +237,13 @@ static inline u8 permission_fault(struct kvm_vcpu *vcp= u, struct kvm_mmu *mmu, return -(u32)fault & errcode; } =20 +bool __kvm_mmu_honors_guest_mtrrs(bool vm_has_noncoherent_dma); + +static inline bool kvm_mmu_honors_guest_mtrrs(struct kvm *kvm) +{ + return __kvm_mmu_honors_guest_mtrrs(kvm_arch_has_noncoherent_dma(kv= m)); +} + void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end); =20 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 f7901cb4d2fa..5d3dc7119e57 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4479,21 +4479,28 @@ static int kvm_tdp_mmu_page_fault(struct kvm_vcpu *= vcpu, } #endif =20 +bool __kvm_mmu_honors_guest_mtrrs(bool vm_has_noncoherent_dma) +{ + /* + * If host MTRRs are ignored (shadow_memtype_mask is non-zero), and= the + * VM has non-coherent DMA (DMA doesn't snoop CPU caches), KVM's AB= I is + * to honor the memtype from the guest's MTRRs so that guest access= es + * to memory that is DMA'd aren't cached against the guest's wishes= . + * + * Note, KVM may still ultimately ignore guest MTRRs for certain PF= Ns, + * e.g. KVM will force UC memtype for host MMIO. + */ + return vm_has_noncoherent_dma && shadow_memtype_mask; +} + int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault= ) { /* * If the guest's MTRRs may be used to compute the "real" memtype, * restrict the mapping level to ensure KVM uses a consistent memty= pe - * across the entire mapping. If the host MTRRs are ignored by TDP - * (shadow_memtype_mask is non-zero), and the VM has non-coherent D= MA - * (DMA doesn't snoop CPU caches), KVM's ABI is to honor the memtyp= e - * from the guest's MTRRs so that guest accesses to memory that is - * DMA'd aren't cached against the guest's wishes. - * - * Note, KVM may still ultimately ignore guest MTRRs for certain PF= Ns, - * e.g. KVM will force UC memtype for host MMIO. + * across the entire mapping. */ - if (shadow_memtype_mask && kvm_arch_has_noncoherent_dma(vcpu->kvm))= { + if (kvm_mmu_honors_guest_mtrrs(vcpu->kvm)) { for ( ; fault->max_level > PG_LEVEL_4K; --fault->max_level)= { int page_num =3D KVM_PAGES_PER_HPAGE(fault->max_lev= el); gfn_t base =3D gfn_round_for_level(fault->gfn,