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Subject[PATCH v3 2/2] arm64: kvm: Introduce MTE VCPU feature
Date
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)) {
+ /*
+ * 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
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