Re: [PATCH v2 2/2] arm64: kvm: Introduce MTE VCPU feature
From: Andrew Jones
Date: Wed Sep 09 2020 - 11:50:14 EST
On Fri, Sep 04, 2020 at 05:00:18PM +0100, Steven Price wrote:
> Add a new VCPU features 'KVM_ARM_VCPU_MTE' which enables memory tagging
> on a VCPU. When enabled on any VCPU in the virtual machine this causes
> all pages that are faulted into the VM to have the PG_mte_tagged flag
> set (and the tag storage cleared if this is the first use).
>
> Signed-off-by: Steven Price <steven.price@xxxxxxx>
> ---
> arch/arm64/include/asm/kvm_emulate.h | 3 +++
> arch/arm64/include/asm/kvm_host.h | 5 ++++-
> arch/arm64/include/uapi/asm/kvm.h | 1 +
> arch/arm64/kvm/mmu.c | 15 +++++++++++++++
> arch/arm64/kvm/reset.c | 8 ++++++++
> arch/arm64/kvm/sys_regs.c | 6 +++++-
> 6 files changed, 36 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index 49a55be2b9a2..0042323a4b7f 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 (test_bit(KVM_ARM_VCPU_MTE, vcpu->arch.features))
> + 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..b1190366242b 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -37,7 +37,7 @@
>
> #define KVM_MAX_VCPUS VGIC_V3_MAX_CPUS
>
> -#define KVM_VCPU_MAX_FEATURES 7
> +#define KVM_VCPU_MAX_FEATURES 8
>
> #define KVM_REQ_SLEEP \
> KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> @@ -110,6 +110,9 @@ struct kvm_arch {
> * supported.
> */
> bool return_nisv_io_abort_to_user;
> +
> + /* If any VCPU has MTE enabled then all memory must be MTE enabled */
> + bool vcpu_has_mte;
It looks like this is unnecessary as it's only used once, where a feature
check could be used.
> };
>
> struct kvm_vcpu_fault_info {
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index ba85bb23f060..2677e1ab8c16 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -106,6 +106,7 @@ struct kvm_regs {
> #define KVM_ARM_VCPU_SVE 4 /* enable SVE for this CPU */
> #define KVM_ARM_VCPU_PTRAUTH_ADDRESS 5 /* VCPU uses address authentication */
> #define KVM_ARM_VCPU_PTRAUTH_GENERIC 6 /* VCPU uses generic authentication */
> +#define KVM_ARM_VCPU_MTE 7 /* VCPU supports Memory Tagging */
>
> struct kvm_vcpu_init {
> __u32 target;
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index ba00bcc0c884..e8891bacd76f 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.vcpu_has_mte && pfn_valid(pfn)) {
> + /*
> + * 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/reset.c b/arch/arm64/kvm/reset.c
> index ee33875c5c2a..82f3883d717f 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -274,6 +274,14 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
> }
> }
>
> + if (test_bit(KVM_ARM_VCPU_MTE, vcpu->arch.features)) {
> + if (!system_supports_mte()) {
> + ret = -EINVAL;
> + goto out;
> + }
> + vcpu->kvm->arch.vcpu_has_mte = true;
> + }
We either need a KVM cap or a new CPU feature probing interface to avoid
making userspace try features one at a time. It's too bad that VCPU_INIT
doesn't clear all offending features from the feature set when returning
EINVAL, because then userspace could create a scratch VCPU with everything
it supports in order to see what KVM also supports in one go.
> +
> switch (vcpu->arch.target) {
> default:
> if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) {
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index a655f172b5ad..6a971b201e81 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 (!test_bit(KVM_ARM_VCPU_MTE, vcpu->arch.features))
> + 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 (test_bit(KVM_ARM_VCPU_MTE, vcpu->arch.features))
> + return 0;
> +
> return REG_HIDDEN_USER | REG_HIDDEN_GUEST;
> }
>
> --
> 2.20.1
>
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>
Thanks,
drew