[PATCH v2 2/2] arm64: kvm: Introduce MTE VCPU feature
Steven Price
steven.price at arm.com
Thu Sep 10 05:21:07 EDT 2020
On 09/09/2020 16:48, Andrew Jones wrote:
> 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 at arm.com>
>> ---
>> 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.
It's used in user_mem_abort(), so every time we fault a page into the VM
- so having to iterate over all VCPUs to check if any have the feature
bit set seems too expensive.
Although perhaps I should just accept that this is realistically a VM
setting and move it out of the VCPU.
>> };
>>
>> 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.
If Peter's TELL_ME_WHAT_YOU_HAVE idea works out then perhaps we don't
need the cap? Or would it still be useful?
Thanks,
Steve
>> +
>> 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
>>
>> _______________________________________________
>> kvmarm mailing list
>> kvmarm at lists.cs.columbia.edu
>> https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
>>
>
> Thanks,
> drew
>
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