| Message ID | 20230714065006.20201-1-yan.y.zhao@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86/mmu: refine memtype related mmu zap | expand |
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@google.com> > Signed-off-by: Yan Zhao <yan.y.zhao@intel.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" ? > +{ > + /* > + * If the TDP is enabled, the host MTRRs are ignored by TDP > + * (shadow_memtype_mask is non-zero), and the VM has non-coherent DMA > + * (DMA doesn't snoop CPU caches), KVM's ABI is to honor the memtype > + * 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 PFNs, > + * e.g. KVM will force UC memtype for host MMIO. > + */ > + return vm_has_noncoherent_dma && tdp_enabled && shadow_memtype_mask; > +} > + > int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault) > { > /*
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@google.com> > > Signed-off-by: Yan Zhao <yan.y.zhao@intel.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!
On Mon, Oct 09, 2023, Sean Christopherson wrote: > On Sat, Oct 07, 2023, Like Xu wrote: > > On 14/7/2023 2:50 pm, 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_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! Gah, and I gave more bad advice when I suggested this idea. There's no need 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 corrupt 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 it 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 honored 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/stops https://github.com/kvm-x86/linux/commit/b344d331adeb [5/5] KVM: VMX: drop IPAT in memtype when CD=1 for KVM_X86_QUIRK_CD_NW_CLEARED https://github.com/kvm-x86/linux/commit/a4d14445c47d commit ec1d8217d59bd7cb03ae4e80551fee987be98a4e Author: Yan Zhao <yan.y.zhao@intel.com> Date: Fri Jul 14 14:50:06 2023 +0800 KVM: x86/mmu: Add helpers to return if KVM honors guest MTRRs Add helpers to check if KVM honors guest MTRRs instead of open coding the logic in kvm_tdp_page_fault(). Future fixes and cleanups will also need to determine if KVM should honor guest MTRRs, e.g. for CR0.CD toggling and and non-coherent DMA transitions. Provide an inner helper, __kvm_mmu_honors_guest_mtrrs(), so that KVM can if guest MTRRs were honored when stopping non-coherent DMA. Note, there is no need to explicitly check that TDP is enabled, KVM clears shadow_memtype_mask when TDP is disabled, i.e. it's non-zero if and only if EPT is enabled. Suggested-by: Sean Christopherson <seanjc@google.com> Signed-off-by: Yan Zhao <yan.y.zhao@intel.com> 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 changelog] Signed-off-by: Sean Christopherson <seanjc@google.com> 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 *vcpu, struct kvm_mmu *mmu, return -(u32)fault & errcode; } +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(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 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 +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 ABI is + * to honor the memtype 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 PFNs, + * 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 memtype - * across the entire mapping. If the host MTRRs are ignored by TDP - * (shadow_memtype_mask is non-zero), and the VM has non-coherent DMA - * (DMA doesn't snoop CPU caches), KVM's ABI is to honor the memtype - * 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 PFNs, - * 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 = KVM_PAGES_PER_HPAGE(fault->max_level); gfn_t base = gfn_round_for_level(fault->gfn,
On Mon, Oct 09, 2023, Sean Christopherson wrote: > On Mon, Oct 09, 2023, Sean Christopherson wrote: > > On Sat, Oct 07, 2023, Like Xu wrote: > > > On 14/7/2023 2:50 pm, 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_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! > > Gah, and I gave more bad advice when I suggested this idea. There's no need 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 corrupt > 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 it > looks sane/acceptable to you? > > New hashes (assuming I didn't botch things and need even more fixup). Oof, today is not my day. I forgot to fix the missing "check" in the changelog that Yan reported. So *these* are the new hashes, barring yet another goof on my end. [1/5] KVM: x86/mmu: Add helpers to return if KVM honors guest MTRRs https://github.com/kvm-x86/linux/commit/1affe455d66d [2/5] KVM: x86/mmu: Zap SPTEs when CR0.CD is toggled iff guest MTRRs are honored https://github.com/kvm-x86/linux/commit/7a18c7c2b69a [3/5] KVM: x86/mmu: Zap SPTEs on MTRR update iff guest MTRRs are honored https://github.com/kvm-x86/linux/commit/9a3768191d95 [4/5] KVM: x86/mmu: Zap KVM TDP when noncoherent DMA assignment starts/stops https://github.com/kvm-x86/linux/commit/68c320298404 [5/5] KVM: VMX: drop IPAT in memtype when CD=1 for KVM_X86_QUIRK_CD_NW_CLEARED https://github.com/kvm-x86/linux/commit/8925b3194512
On Mon, Oct 09, 2023 at 02:27:16PM -0700, Sean Christopherson wrote: > On Mon, Oct 09, 2023, Sean Christopherson wrote: > > On Sat, Oct 07, 2023, Like Xu wrote: > > > On 14/7/2023 2:50 pm, 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_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! > > Gah, and I gave more bad advice when I suggested this idea. There's no need 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 corrupt > 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 it > looks sane/acceptable to you? yes, tested working on my side. I think why we added the checking of tdp_enabled was because of the existing check in patch 3. As noncoherent DMAs checking is not on hot paths, the previous double checking is also good :) BTW, as param "kvm" is now removed from the helper, better to remove the word "second" in comment in patch 4, i.e. - * So, specify the second parameter as true here to indicate - * non-coherent DMAs are/were involved and TDP zap might be - * necessary. + * So, specify the parameter as true here to indicate non-coherent + * DMAs are/were involved and TDP zap might be necessary. Sorry and thanks a lot for helps on this series!
On Tue, Oct 10, 2023, Yan Zhao wrote: > BTW, as param "kvm" is now removed from the helper, better to remove the word > "second" in comment in patch 4, i.e. > > - * So, specify the second parameter as true here to indicate > - * non-coherent DMAs are/were involved and TDP zap might be > - * necessary. > + * So, specify the parameter as true here to indicate non-coherent > + * DMAs are/were involved and TDP zap might be necessary. > > Sorry and thanks a lot for helps on this series! Heh, don't be sorry, it's not your fault I can't get this quite right. Fixed up yet again, hopefully for the last time. This is what I ended up with for the comment: /* * Non-coherent DMA assignment and de-assignment will affect * whether KVM honors guest MTRRs and cause changes in memtypes * in TDP. * So, pass %true unconditionally to indicate non-coherent DMA was, * or will be involved, and that zapping SPTEs might be necessary. */ and the hashes: [1/5] KVM: x86/mmu: Add helpers to return if KVM honors guest MTRRs https://github.com/kvm-x86/linux/commit/1affe455d66d [2/5] KVM: x86/mmu: Zap SPTEs when CR0.CD is toggled iff guest MTRRs are honored https://github.com/kvm-x86/linux/commit/7a18c7c2b69a [3/5] KVM: x86/mmu: Zap SPTEs on MTRR update iff guest MTRRs are honored https://github.com/kvm-x86/linux/commit/9a3768191d95 [4/5] KVM: x86/mmu: Zap KVM TDP when noncoherent DMA assignment starts/stops https://github.com/kvm-x86/linux/commit/362ff6dca541 [5/5] KVM: VMX: drop IPAT in memtype when CD=1 for KVM_X86_QUIRK_CD_NW_CLEARED https://github.com/kvm-x86/linux/commit/c9f65a3f2d92
On Tue, Oct 10, 2023 at 05:08:08PM -0700, Sean Christopherson wrote: > On Tue, Oct 10, 2023, Yan Zhao wrote: > > BTW, as param "kvm" is now removed from the helper, better to remove the word > > "second" in comment in patch 4, i.e. > > > > - * So, specify the second parameter as true here to indicate > > - * non-coherent DMAs are/were involved and TDP zap might be > > - * necessary. > > + * So, specify the parameter as true here to indicate non-coherent > > + * DMAs are/were involved and TDP zap might be necessary. > > > > Sorry and thanks a lot for helps on this series! > > Heh, don't be sorry, it's not your fault I can't get this quite right. Fixed > up yet again, hopefully for the last time. This is what I ended up with for the > comment: > > /* > * Non-coherent DMA assignment and de-assignment will affect > * whether KVM honors guest MTRRs and cause changes in memtypes > * in TDP. > * So, pass %true unconditionally to indicate non-coherent DMA was, > * or will be involved, and that zapping SPTEs might be necessary. > */ > > and the hashes: > > [1/5] KVM: x86/mmu: Add helpers to return if KVM honors guest MTRRs > https://github.com/kvm-x86/linux/commit/1affe455d66d > [2/5] KVM: x86/mmu: Zap SPTEs when CR0.CD is toggled iff guest MTRRs are honored > https://github.com/kvm-x86/linux/commit/7a18c7c2b69a > [3/5] KVM: x86/mmu: Zap SPTEs on MTRR update iff guest MTRRs are honored > https://github.com/kvm-x86/linux/commit/9a3768191d95 > [4/5] KVM: x86/mmu: Zap KVM TDP when noncoherent DMA assignment starts/stops > https://github.com/kvm-x86/linux/commit/362ff6dca541 > [5/5] KVM: VMX: drop IPAT in memtype when CD=1 for KVM_X86_QUIRK_CD_NW_CLEARED > https://github.com/kvm-x86/linux/commit/c9f65a3f2d92 Looks good to me, thanks!
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) +{ + /* + * If the TDP is enabled, the host MTRRs are ignored by TDP + * (shadow_memtype_mask is non-zero), and the VM has non-coherent DMA + * (DMA doesn't snoop CPU caches), KVM's ABI is to honor the memtype + * 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 PFNs, + * e.g. KVM will force UC memtype for host MMIO. + */ + return vm_has_noncoherent_dma && tdp_enabled && shadow_memtype_mask; +} + int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault) { /*
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@google.com> Signed-off-by: Yan Zhao <yan.y.zhao@intel.com> --- arch/x86/kvm/mmu.h | 7 +++++++ arch/x86/kvm/mmu/mmu.c | 15 +++++++++++++++ 2 files changed, 22 insertions(+)