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Subject[PATCH v8 2/5] 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 | 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 11beda85ee7e..302ebc61d8ac 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 {
@@ -745,6 +747,7 @@ 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 7d2257cc5438..6076a1ab41d9 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));
+ }
+ }
+
if (writable) {
prot |= KVM_PGTABLE_PROT_W;
kvm_set_pfn_dirty(pfn);
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 3313dedfa505..bb5525bbf1ca 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1029,7 +1029,8 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
val &= ~(0xfUL << ID_AA64PFR0_CSV3_SHIFT);
val |= ((u64)vcpu->kvm->arch.pfr0_csv3 << ID_AA64PFR0_CSV3_SHIFT);
} else if (id == SYS_ID_AA64PFR1_EL1) {
- val &= ~(0xfUL << ID_AA64PFR1_MTE_SHIFT);
+ if (!kvm_has_mte(vcpu->kvm))
+ 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) |
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 886802b8ffba..de737d5102ca 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1056,6 +1056,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_ENFORCE_PV_FEATURE_CPUID 190
#define KVM_CAP_SYS_HYPERV_CPUID 191
#define KVM_CAP_DIRTY_LOG_RING 192
+#define KVM_CAP_ARM_MTE 193

#ifdef KVM_CAP_IRQ_ROUTING

--
2.20.1
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