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[34.82.80.254]) by smtp.gmail.com with ESMTPSA id o1-20020a637e41000000b003804d0e2c9esm14104960pgn.35.2022.04.05.15.46.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 05 Apr 2022 15:46:47 -0700 (PDT) Date: Tue, 5 Apr 2022 22:46:43 +0000 From: David Matlack To: Ben Gardon Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Paolo Bonzini , Peter Xu , Sean Christopherson , Jim Mattson , David Dunn , Jing Zhang , Junaid Shahid Subject: Re: [PATCH v3 08/11] KVM: x86/MMU: Allow NX huge pages to be disabled on a per-vm basis Message-ID: References: <20220330174621.1567317-1-bgardon@google.com> <20220330174621.1567317-9-bgardon@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220330174621.1567317-9-bgardon@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 30, 2022 at 10:46:18AM -0700, Ben Gardon wrote: > In some cases, the NX hugepage mitigation for iTLB multihit is not > needed for all guests on a host. Allow disabling the mitigation on a > per-VM basis to avoid the performance hit of NX hugepages on trusted > workloads. > > Signed-off-by: Ben Gardon Reviewed-by: David Matlack > --- > Documentation/virt/kvm/api.rst | 11 +++++++++++ > arch/x86/include/asm/kvm_host.h | 2 ++ > arch/x86/kvm/mmu.h | 10 ++++++---- > arch/x86/kvm/mmu/mmu.c | 2 +- > arch/x86/kvm/mmu/spte.c | 7 ++++--- > arch/x86/kvm/mmu/spte.h | 3 ++- > arch/x86/kvm/mmu/tdp_mmu.c | 3 ++- > arch/x86/kvm/x86.c | 6 ++++++ > include/uapi/linux/kvm.h | 1 + > 9 files changed, 35 insertions(+), 10 deletions(-) > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst > index b102ba7cf903..b40c3113b14b 100644 > --- a/Documentation/virt/kvm/api.rst > +++ b/Documentation/virt/kvm/api.rst > @@ -7844,6 +7844,17 @@ At this time, KVM_PMU_CAP_DISABLE is the only capability. Setting > this capability will disable PMU virtualization for that VM. Usermode > should adjust CPUID leaf 0xA to reflect that the PMU is disabled. > > +8.36 KVM_CAP_VM_DISABLE_NX_HUGE_PAGES > +--------------------------- > + > +:Capability KVM_CAP_PMU_CAPABILITY > +:Architectures: x86 > +:Type: vm > + > +This capability disables the NX huge pages mitigation for iTLB MULTIHIT. > + > +The capability has no effect if the nx_huge_pages module parameter is not set. > + > 9. Known KVM API problems > ========================= > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 676705ad1e23..dcff7709444d 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -1246,6 +1246,8 @@ struct kvm_arch { > hpa_t hv_root_tdp; > spinlock_t hv_root_tdp_lock; > #endif > + > + bool disable_nx_huge_pages; > }; > > struct kvm_vm_stat { > diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h > index e6cae6f22683..69cffc86b888 100644 > --- a/arch/x86/kvm/mmu.h > +++ b/arch/x86/kvm/mmu.h > @@ -173,10 +173,12 @@ struct kvm_page_fault { > int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault); > > extern int nx_huge_pages; > -static inline bool is_nx_huge_page_enabled(void) > +static inline bool is_nx_huge_page_enabled(struct kvm *kvm) > { > - return READ_ONCE(nx_huge_pages); > + return READ_ONCE(nx_huge_pages) && > + !kvm->arch.disable_nx_huge_pages; > } > +void kvm_update_nx_huge_pages(struct kvm *kvm); > > static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, > u32 err, bool prefetch) > @@ -191,8 +193,8 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, > .user = err & PFERR_USER_MASK, > .prefetch = prefetch, > .is_tdp = likely(vcpu->arch.mmu->page_fault == kvm_tdp_page_fault), > - .nx_huge_page_workaround_enabled = is_nx_huge_page_enabled(), > - > + .nx_huge_page_workaround_enabled = > + is_nx_huge_page_enabled(vcpu->kvm), > .max_level = KVM_MAX_HUGEPAGE_LEVEL, > .req_level = PG_LEVEL_4K, > .goal_level = PG_LEVEL_4K, > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index af428cb65b3f..eb7b935d3caa 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -6202,7 +6202,7 @@ static void __set_nx_huge_pages(bool val) > nx_huge_pages = itlb_multihit_kvm_mitigation = val; > } > > -static void kvm_update_nx_huge_pages(struct kvm *kvm) > +void kvm_update_nx_huge_pages(struct kvm *kvm) > { > mutex_lock(&kvm->slots_lock); > kvm_mmu_zap_all_fast(kvm); > diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c > index 4739b53c9734..877ad30bc7ad 100644 > --- a/arch/x86/kvm/mmu/spte.c > +++ b/arch/x86/kvm/mmu/spte.c > @@ -116,7 +116,7 @@ bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, > spte |= spte_shadow_accessed_mask(spte); > > if (level > PG_LEVEL_4K && (pte_access & ACC_EXEC_MASK) && > - is_nx_huge_page_enabled()) { > + is_nx_huge_page_enabled(vcpu->kvm)) { > pte_access &= ~ACC_EXEC_MASK; > } > > @@ -215,7 +215,8 @@ static u64 make_spte_executable(u64 spte) > * This is used during huge page splitting to build the SPTEs that make up the > * new page table. > */ > -u64 make_huge_page_split_spte(u64 huge_spte, int huge_level, int index) > +u64 make_huge_page_split_spte(struct kvm *kvm, u64 huge_spte, int huge_level, > + int index) > { > u64 child_spte; > int child_level; > @@ -243,7 +244,7 @@ u64 make_huge_page_split_spte(u64 huge_spte, int huge_level, int index) > * When splitting to a 4K page, mark the page executable as the > * NX hugepage mitigation no longer applies. > */ > - if (is_nx_huge_page_enabled()) > + if (is_nx_huge_page_enabled(kvm)) > child_spte = make_spte_executable(child_spte); > } > > diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h > index 73f12615416f..e4142caff4b1 100644 > --- a/arch/x86/kvm/mmu/spte.h > +++ b/arch/x86/kvm/mmu/spte.h > @@ -415,7 +415,8 @@ bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, > unsigned int pte_access, gfn_t gfn, kvm_pfn_t pfn, > u64 old_spte, bool prefetch, bool can_unsync, > bool host_writable, u64 *new_spte); > -u64 make_huge_page_split_spte(u64 huge_spte, int huge_level, int index); > +u64 make_huge_page_split_spte(struct kvm *kvm, u64 huge_spte, int huge_level, > + int index); > u64 make_nonleaf_spte(u64 *child_pt, bool ad_disabled); > u64 make_mmio_spte(struct kvm_vcpu *vcpu, u64 gfn, unsigned int access); > u64 mark_spte_for_access_track(u64 spte); > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > index a2f9a34a0168..5d82a54924e6 100644 > --- a/arch/x86/kvm/mmu/tdp_mmu.c > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > @@ -1469,7 +1469,8 @@ static int tdp_mmu_split_huge_page(struct kvm *kvm, struct tdp_iter *iter, > * not been linked in yet and thus is not reachable from any other CPU. > */ > for (i = 0; i < PT64_ENT_PER_PAGE; i++) > - sp->spt[i] = make_huge_page_split_spte(huge_spte, level, i); > + sp->spt[i] = make_huge_page_split_spte(kvm, huge_spte, > + level, i); > > /* > * Replace the huge spte with a pointer to the populated lower level > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 7a066cf92692..ea1d620b35df 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -4268,6 +4268,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) > case KVM_CAP_SYS_ATTRIBUTES: > case KVM_CAP_VAPIC: > case KVM_CAP_ENABLE_CAP: > + case KVM_CAP_VM_DISABLE_NX_HUGE_PAGES: > r = 1; > break; > case KVM_CAP_EXIT_HYPERCALL: > @@ -6061,6 +6062,11 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, > } > mutex_unlock(&kvm->lock); > break; > + case KVM_CAP_VM_DISABLE_NX_HUGE_PAGES: > + kvm->arch.disable_nx_huge_pages = true; > + kvm_update_nx_huge_pages(kvm); > + r = 0; > + break; > default: > r = -EINVAL; > break; > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > index 8616af85dc5d..12399c969b42 100644 > --- a/include/uapi/linux/kvm.h > +++ b/include/uapi/linux/kvm.h > @@ -1145,6 +1145,7 @@ struct kvm_ppc_resize_hpt { > #define KVM_CAP_PMU_CAPABILITY 212 > #define KVM_CAP_DISABLE_QUIRKS2 213 > #define KVM_CAP_VM_TSC_CONTROL 214 > +#define KVM_CAP_VM_DISABLE_NX_HUGE_PAGES 215 > > #ifdef KVM_CAP_IRQ_ROUTING > > -- > 2.35.1.1021.g381101b075-goog >