[RFC PATCH 2/2] arm64: kvm: Introduce MTE VCPU feature

[Steven Price <steven.price@arm.com>]

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@arm.com>
---
 arch/arm64/include/asm/kvm_emulate.h |  3 +++
 arch/arm64/include/asm/kvm_host.h    |  2 +-
 arch/arm64/include/uapi/asm/kvm.h    |  1 +
 arch/arm64/kvm/reset.c               |  8 ++++++++
 arch/arm64/kvm/sys_regs.c            |  3 ++-
 virt/kvm/arm/mmu.c                   | 11 +++++++++++
 6 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index a30b4eec7cb4..b118f466a40b 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 1f10e9dee2e0..3461639bb08a 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)
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/reset.c b/arch/arm64/kvm/reset.c
index ab76728e2742..f87a434c0849 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -287,6 +287,14 @@ 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;
+	}
+
 	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 3ae008a9b0bd..a6a9552d1233 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1096,7 +1096,8 @@ 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) |
diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
index e3b9ee268823..040a7fffaa93 100644
--- a/virt/kvm/arm/mmu.c
+++ b/virt/kvm/arm/mmu.c
@@ -1783,6 +1783,17 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 			vma_pagesize = PMD_SIZE;
 	}
 
+	if (system_supports_mte() && kvm->arch.vcpu_has_mte) {
+		/*
+		 * 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);
+
+		if (!test_and_set_bit(PG_mte_tagged, &page->flags))
+			mte_clear_page_tags(page_address(page), page_size(page));
+	}
+
 	if (writable)
 		kvm_set_pfn_dirty(pfn);
 
-- 
2.20.1