Messages in this thread | | | Subject | Re: [PATCH v9 2/6] arm64: kvm: Introduce MTE VM feature | From | Steven Price <> | Date | Wed, 10 Mar 2021 14:52:49 +0000 |
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On 09/03/2021 17:06, Marc Zyngier wrote: > On Mon, 01 Mar 2021 14:23:11 +0000, > Steven Price <steven.price@arm.com> wrote: >> >> Add a new VM feature 'KVM_ARM_CAP_MTE' which enables memory tagging >> for a VM. This will expose the feature to the guest and automatically >> tag memory pages touched by the VM as PG_mte_tagged (and clear the tag >> storage) to ensure that the guest cannot see stale tags, and so that >> the tags are correctly saved/restored across swap. >> >> Actually exposing the new capability to user space happens in a later >> patch. >> >> 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/hyp/exception.c | 3 ++- >> arch/arm64/kvm/mmu.c | 16 ++++++++++++++++ >> arch/arm64/kvm/sys_regs.c | 3 ++- >> include/uapi/linux/kvm.h | 1 + >> 6 files changed, 27 insertions(+), 2 deletions(-) >> >> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h >> index f612c090f2e4..6bf776c2399c 100644 >> --- a/arch/arm64/include/asm/kvm_emulate.h >> +++ b/arch/arm64/include/asm/kvm_emulate.h >> @@ -84,6 +84,9 @@ 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 (kvm_has_mte(vcpu->kvm)) >> + 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 3d10e6527f7d..1170ee137096 100644 >> --- a/arch/arm64/include/asm/kvm_host.h >> +++ b/arch/arm64/include/asm/kvm_host.h >> @@ -132,6 +132,8 @@ struct kvm_arch { >> >> u8 pfr0_csv2; >> u8 pfr0_csv3; >> + /* Memory Tagging Extension enabled for the guest */ >> + bool mte_enabled; >> }; >> >> struct kvm_vcpu_fault_info { >> @@ -767,6 +769,7 @@ bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu); >> #define kvm_arm_vcpu_sve_finalized(vcpu) \ >> ((vcpu)->arch.flags & KVM_ARM64_VCPU_SVE_FINALIZED) >> >> +#define kvm_has_mte(kvm) (system_supports_mte() && (kvm)->arch.mte_enabled) >> #define kvm_vcpu_has_pmu(vcpu) \ >> (test_bit(KVM_ARM_VCPU_PMU_V3, (vcpu)->arch.features)) >> >> diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c >> index 73629094f903..56426565600c 100644 >> --- a/arch/arm64/kvm/hyp/exception.c >> +++ b/arch/arm64/kvm/hyp/exception.c >> @@ -112,7 +112,8 @@ static void enter_exception64(struct kvm_vcpu *vcpu, unsigned long target_mode, >> new |= (old & PSR_C_BIT); >> new |= (old & PSR_V_BIT); >> >> - // TODO: TCO (if/when ARMv8.5-MemTag is exposed to guests) >> + if (kvm_has_mte(vcpu->kvm)) >> + new |= PSR_TCO_BIT; >> >> new |= (old & PSR_DIT_BIT); >> >> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c >> index 77cb2d28f2a4..fdb6ab604fd0 100644 >> --- a/arch/arm64/kvm/mmu.c >> +++ b/arch/arm64/kvm/mmu.c >> @@ -879,6 +879,22 @@ 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 (kvm_has_mte(kvm) && pfn_valid(pfn)) { >> + /* >> + * VM will be able to see the page's tags, so we must ensure >> + * they have been initialised. if PG_mte_tagged is set, tags >> + * have already been initialised. >> + */ >> + struct page *page = pfn_to_page(pfn); >> + unsigned long i, nr_pages = vma_pagesize >> PAGE_SHIFT; >> + >> + 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)); >> + } >> + } > > Is there any reason to do this dance for anything but a translation > fault?
Good point I guess this should have a (fault_status != FSC_PERM) in the test to match the other paths.
>> + >> if (writable) >> prot |= KVM_PGTABLE_PROT_W; >> >> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c >> index 4f2f1e3145de..e09dbc00b0a2 100644 >> --- a/arch/arm64/kvm/sys_regs.c >> +++ b/arch/arm64/kvm/sys_regs.c >> @@ -1046,7 +1046,8 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu, >> val |= FIELD_PREP(FEATURE(ID_AA64PFR0_CSV3), (u64)vcpu->kvm->arch.pfr0_csv3); >> break; >> case SYS_ID_AA64PFR1_EL1: >> - val &= ~FEATURE(ID_AA64PFR1_MTE); >> + if (!kvm_has_mte(vcpu->kvm)) >> + val &= ~FEATURE(ID_AA64PFR1_MTE); > > Are we happy to expose *any* of the MTE flavours? Or should we > restrict it in any way?
Another good point - it would make sense to restrict this in case another MTE flavour is invented.
Thanks,
Steve
>> break; >> case SYS_ID_AA64ISAR1_EL1: >> if (!vcpu_has_ptrauth(vcpu)) >> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h >> index 8b281f722e5b..05618a4abf7e 100644 >> --- a/include/uapi/linux/kvm.h >> +++ b/include/uapi/linux/kvm.h >> @@ -1078,6 +1078,7 @@ struct kvm_ppc_resize_hpt { >> #define KVM_CAP_DIRTY_LOG_RING 192 >> #define KVM_CAP_X86_BUS_LOCK_EXIT 193 >> #define KVM_CAP_PPC_DAWR1 194 >> +#define KVM_CAP_ARM_MTE 195 >> >> #ifdef KVM_CAP_IRQ_ROUTING >> >> -- >> 2.20.1 >> >> > > Thanks, > > M. >
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