Messages in this thread | | | Subject | Re: [PATCH v3 2/2] arm64: kvm: Introduce MTE VCPU feature | From | Steven Price <> | Date | Fri, 2 Oct 2020 16:30:47 +0100 |
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On 02/10/2020 15:30, Andrew Jones wrote: > On Fri, Sep 25, 2020 at 10:36:07AM +0100, Steven Price wrote: >> Add a new VM feature 'KVM_ARM_CAP_MTE' which enables memory tagging >> for a VM. This exposes the feature to the guest and automatically tags >> memory pages touched by the VM as PG_mte_tagged (and clears the tags >> storage) to ensure that the guest cannot see stale tags, and so that the >> tags are correctly saved/restored across swap. >> >> Signed-off-by: Steven Price <steven.price@arm.com> >> --- >> arch/arm64/include/asm/kvm_emulate.h | 3 +++ >> arch/arm64/include/asm/kvm_host.h | 3 +++ >> arch/arm64/kvm/arm.c | 9 +++++++++ >> arch/arm64/kvm/mmu.c | 15 +++++++++++++++ >> arch/arm64/kvm/sys_regs.c | 6 +++++- >> include/uapi/linux/kvm.h | 1 + >> 6 files changed, 36 insertions(+), 1 deletion(-) >> >> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h >> index 49a55be2b9a2..4923a566ae6e 100644 >> --- a/arch/arm64/include/asm/kvm_emulate.h >> +++ b/arch/arm64/include/asm/kvm_emulate.h >> @@ -79,6 +79,9 @@ static inline void vcpu_reset_hcr(struct kvm_vcpu *vcpu) >> if (cpus_have_const_cap(ARM64_MISMATCHED_CACHE_TYPE) || >> vcpu_el1_is_32bit(vcpu)) >> vcpu->arch.hcr_el2 |= HCR_TID2; >> + >> + if (vcpu->kvm->arch.mte_enabled) >> + vcpu->arch.hcr_el2 |= HCR_ATA; >> } >> >> static inline unsigned long *vcpu_hcr(struct kvm_vcpu *vcpu) >> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h >> index 4f4360dd149e..1379300c1487 100644 >> --- a/arch/arm64/include/asm/kvm_host.h >> +++ b/arch/arm64/include/asm/kvm_host.h >> @@ -110,6 +110,9 @@ struct kvm_arch { >> * supported. >> */ >> bool return_nisv_io_abort_to_user; >> + >> + /* Memory Tagging Extension enabled for the guest */ >> + bool mte_enabled; >> }; >> >> struct kvm_vcpu_fault_info { >> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c >> index 46dc3d75cf13..624edca0a1fa 100644 >> --- a/arch/arm64/kvm/arm.c >> +++ b/arch/arm64/kvm/arm.c >> @@ -87,6 +87,12 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, >> r = 0; >> kvm->arch.return_nisv_io_abort_to_user = true; >> break; >> + case KVM_CAP_ARM_MTE: >> + if (!system_supports_mte() || kvm->created_vcpus) >> + return -EINVAL; >> + r = 0; >> + kvm->arch.mte_enabled = true; >> + break; >> default: >> r = -EINVAL; >> break; >> @@ -206,6 +212,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) >> */ >> r = 1; >> break; >> + case KVM_CAP_ARM_MTE: >> + r = system_supports_mte(); >> + break; >> default: >> r = kvm_arch_vm_ioctl_check_extension(kvm, ext); >> break; >> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c >> index ba00bcc0c884..befb9e1f0aa6 100644 >> --- a/arch/arm64/kvm/mmu.c >> +++ b/arch/arm64/kvm/mmu.c >> @@ -1949,6 +1949,21 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >> if (vma_pagesize == PAGE_SIZE && !force_pte) >> vma_pagesize = transparent_hugepage_adjust(memslot, hva, >> &pfn, &fault_ipa); >> + if (system_supports_mte() && kvm->arch.mte_enabled && pfn_valid(pfn)) { > > 'system_supports_mte() && kvm->arch.mte_enabled' is redundant, but I > assume system_supports_mte() is there to improve the efficiency of the > branch, as it's using cpus_have_const_cap().
system_supports_mte() compiles to 0 when MTE support isn't built in, so this code can be removed by the compiler, whereas with kvm->arch.mte_enabled I doubt the compiler can deduce that it is never set.
> Maybe a helper like > > static inline bool kvm_arm_mte_enabled(struct kvm *kvm) > { > return system_supports_mte() && kvm->arch.mte_enabled; > } > > would allow both the more efficient branch and look less confusing > where it gets used.
I wasn't sure it was worth having a helper since this was the only place checking this condition. It's also a bit tricky putting this in a logical header file, kvm_host.h doesn't work because struct kvm hasn't been defined by then.
Steve
>> + /* >> + * VM will be able to see the page's tags, so we must ensure >> + * they have been initialised. >> + */ >> + struct page *page = pfn_to_page(pfn); >> + long i, nr_pages = compound_nr(page); >> + >> + /* if PG_mte_tagged is set, tags have already been initialised */ >> + for (i = 0; i < nr_pages; i++, page++) { >> + if (!test_and_set_bit(PG_mte_tagged, &page->flags)) >> + mte_clear_page_tags(page_address(page)); >> + } >> + } >> + >> if (writable) >> kvm_set_pfn_dirty(pfn); >> >> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c >> index a655f172b5ad..5010a47152b4 100644 >> --- a/arch/arm64/kvm/sys_regs.c >> +++ b/arch/arm64/kvm/sys_regs.c >> @@ -1132,7 +1132,8 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu, >> val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT); >> val &= ~(0xfUL << ID_AA64PFR0_AMU_SHIFT); >> } else if (id == SYS_ID_AA64PFR1_EL1) { >> - val &= ~(0xfUL << ID_AA64PFR1_MTE_SHIFT); >> + if (!vcpu->kvm->arch.mte_enabled) >> + val &= ~(0xfUL << ID_AA64PFR1_MTE_SHIFT); >> } else if (id == SYS_ID_AA64ISAR1_EL1 && !vcpu_has_ptrauth(vcpu)) { >> val &= ~((0xfUL << ID_AA64ISAR1_APA_SHIFT) | >> (0xfUL << ID_AA64ISAR1_API_SHIFT) | >> @@ -1394,6 +1395,9 @@ static bool access_mte_regs(struct kvm_vcpu *vcpu, struct sys_reg_params *p, >> static unsigned int mte_visibility(const struct kvm_vcpu *vcpu, >> const struct sys_reg_desc *rd) >> { >> + if (vcpu->kvm->arch.mte_enabled) >> + return 0; >> + >> return REG_HIDDEN_USER | REG_HIDDEN_GUEST; >> } >> >> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h >> index f6d86033c4fa..87678ed82ab4 100644 >> --- a/include/uapi/linux/kvm.h >> +++ b/include/uapi/linux/kvm.h >> @@ -1035,6 +1035,7 @@ struct kvm_ppc_resize_hpt { >> #define KVM_CAP_LAST_CPU 184 >> #define KVM_CAP_SMALLER_MAXPHYADDR 185 >> #define KVM_CAP_S390_DIAG318 186 >> +#define KVM_CAP_ARM_MTE 188 >> >> #ifdef KVM_CAP_IRQ_ROUTING >> >> -- >> 2.20.1 >> >> > > Besides the helper suggestion nit > > Reviewed-by: Andrew Jones <drjones@redhat.com> >
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