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    Subject[PATCH v11 2/6] arm64: kvm: Introduce MTE VM feature
    Date
    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 | 20 ++++++++++++++++++++
    arch/arm64/kvm/sys_regs.c | 3 +++
    include/uapi/linux/kvm.h | 1 +
    6 files changed, 32 insertions(+), 1 deletion(-)

    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..5f8e165ea053 100644
    --- a/arch/arm64/kvm/mmu.c
    +++ b/arch/arm64/kvm/mmu.c
    @@ -879,6 +879,26 @@ 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 (fault_status != FSC_PERM && kvm_has_mte(kvm) && !device &&
    + 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.
    + */
    + unsigned long i, nr_pages = vma_pagesize >> PAGE_SHIFT;
    + struct page *page = pfn_to_online_page(pfn);
    +
    + if (!page)
    + return -EFAULT;
    +
    + 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)
    prot |= KVM_PGTABLE_PROT_W;

    diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
    index 4f2f1e3145de..18c87500a7a8 100644
    --- a/arch/arm64/kvm/sys_regs.c
    +++ b/arch/arm64/kvm/sys_regs.c
    @@ -1047,6 +1047,9 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
    break;
    case SYS_ID_AA64PFR1_EL1:
    val &= ~FEATURE(ID_AA64PFR1_MTE);
    + if (kvm_has_mte(vcpu->kvm))
    + val |= FIELD_PREP(FEATURE(ID_AA64PFR1_MTE),
    + ID_AA64PFR1_MTE);
    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 f6afee209620..6dc16c09a2d1 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
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