| Message ID | 20220321234844.1543161-10-bgardon@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: x86: Add a cap to disable NX hugepages on a VM | expand |
On Mon, Mar 21, 2022 at 04:48:42PM -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 <bgardon@google.com> > --- > arch/x86/include/asm/kvm_host.h | 1 + > arch/x86/kvm/mmu.h | 1 + > arch/x86/kvm/mmu/mmu.c | 6 ++++-- > arch/x86/kvm/x86.c | 6 ++++++ > include/uapi/linux/kvm.h | 1 + > 5 files changed, 13 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 0a0c54639dd8..04ddfc475ce0 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -1242,6 +1242,7 @@ struct kvm_arch { > #endif > > bool nx_huge_pages; > + bool disable_nx_huge_pages; > }; > > struct kvm_vm_stat { > diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h > index dd28fe8d13ae..36d8d84ca6c6 100644 > --- a/arch/x86/kvm/mmu.h > +++ b/arch/x86/kvm/mmu.h > @@ -177,6 +177,7 @@ static inline bool is_nx_huge_page_enabled(struct kvm *kvm) > { > return READ_ONCE(kvm->arch.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) > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index dc9672f70468..a7d387ccfd74 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -6195,9 +6195,10 @@ 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) > { > - kvm->arch.nx_huge_pages = nx_huge_pages; > + kvm->arch.nx_huge_pages = nx_huge_pages && > + !kvm->arch.disable_nx_huge_pages; kvm->arch.nx_huge_pages seems like it could be dropped and is_nx_huge_page_enabled() could just check this condition. > > mutex_lock(&kvm->slots_lock); > kvm_mmu_zap_all_fast(kvm); > @@ -6451,6 +6452,7 @@ int kvm_mmu_post_init_vm(struct kvm *kvm) > int err; > > kvm->arch.nx_huge_pages = READ_ONCE(nx_huge_pages); > + kvm->arch.disable_nx_huge_pages = false; I believe this can be omitted since kvm_arch is zero-initialized. > err = kvm_vm_create_worker_thread(kvm, kvm_nx_lpage_recovery_worker, 0, > "kvm-nx-lpage-recovery", > &kvm->arch.nx_lpage_recovery_thread); > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 51106d32f04e..73df90a6932b 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -4256,6 +4256,7 @@ 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: Please document the new capability. > r = 1; > break; > case KVM_CAP_EXIT_HYPERCALL: > @@ -6048,6 +6049,11 @@ 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 ee5cc9e2a837..6f9fa7ecfd1e 100644 > --- a/include/uapi/linux/kvm.h > +++ b/include/uapi/linux/kvm.h > @@ -1144,6 +1144,7 @@ struct kvm_ppc_resize_hpt { > #define KVM_CAP_S390_MEM_OP_EXTENSION 211 > #define KVM_CAP_PMU_CAPABILITY 212 > #define KVM_CAP_DISABLE_QUIRKS2 213 > +#define KVM_CAP_VM_DISABLE_NX_HUGE_PAGES 214 > > #ifdef KVM_CAP_IRQ_ROUTING > > -- > 2.35.1.894.gb6a874cedc-goog >
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 0a0c54639dd8..04ddfc475ce0 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1242,6 +1242,7 @@ struct kvm_arch { #endif bool nx_huge_pages; + bool disable_nx_huge_pages; }; struct kvm_vm_stat { diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h index dd28fe8d13ae..36d8d84ca6c6 100644 --- a/arch/x86/kvm/mmu.h +++ b/arch/x86/kvm/mmu.h @@ -177,6 +177,7 @@ static inline bool is_nx_huge_page_enabled(struct kvm *kvm) { return READ_ONCE(kvm->arch.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) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index dc9672f70468..a7d387ccfd74 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -6195,9 +6195,10 @@ 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) { - kvm->arch.nx_huge_pages = nx_huge_pages; + kvm->arch.nx_huge_pages = nx_huge_pages && + !kvm->arch.disable_nx_huge_pages; mutex_lock(&kvm->slots_lock); kvm_mmu_zap_all_fast(kvm); @@ -6451,6 +6452,7 @@ int kvm_mmu_post_init_vm(struct kvm *kvm) int err; kvm->arch.nx_huge_pages = READ_ONCE(nx_huge_pages); + kvm->arch.disable_nx_huge_pages = false; err = kvm_vm_create_worker_thread(kvm, kvm_nx_lpage_recovery_worker, 0, "kvm-nx-lpage-recovery", &kvm->arch.nx_lpage_recovery_thread); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 51106d32f04e..73df90a6932b 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4256,6 +4256,7 @@ 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: @@ -6048,6 +6049,11 @@ 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 ee5cc9e2a837..6f9fa7ecfd1e 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -1144,6 +1144,7 @@ struct kvm_ppc_resize_hpt { #define KVM_CAP_S390_MEM_OP_EXTENSION 211 #define KVM_CAP_PMU_CAPABILITY 212 #define KVM_CAP_DISABLE_QUIRKS2 213 +#define KVM_CAP_VM_DISABLE_NX_HUGE_PAGES 214 #ifdef KVM_CAP_IRQ_ROUTING
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 <bgardon@google.com> --- arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/mmu.h | 1 + arch/x86/kvm/mmu/mmu.c | 6 ++++-- arch/x86/kvm/x86.c | 6 ++++++ include/uapi/linux/kvm.h | 1 + 5 files changed, 13 insertions(+), 2 deletions(-)