Re: [PATCH 3/3] KVM: arm64: Use per guest ID register for ID_AA64PFR1_EL1.MTE

With per guest ID registers, MTE settings from userspace can be stored in
its corresponding ID register.

No functional change intended.

Signed-off-by: Suraj Jitindar Singh <redacted>
---
 arch/arm64/include/asm/kvm_host.h | 21 ++++++++++-----------
 arch/arm64/kvm/arm.c              | 11 ++++++++++-
 arch/arm64/kvm/sys_regs.c         |  5 +++++
 3 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 7b0f43373dbe..861997a14ba1 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h

@@ -226,9 +226,7 @@ struct kvm_arch {
 	 */
 #define KVM_ARCH_FLAG_RETURN_NISV_IO_ABORT_TO_USER	0
 	/* Memory Tagging Extension enabled for the guest */
-#define KVM_ARCH_FLAG_MTE_ENABLED			1
-	/* At least one vCPU has ran in the VM */
-#define KVM_ARCH_FLAG_HAS_RAN_ONCE			2
+#define KVM_ARCH_FLAG_HAS_RAN_ONCE			1
 	/*
 	 * The following two bits are used to indicate the guest's EL1
 	 * register width configuration. A value of KVM_ARCH_FLAG_EL1_32BIT

@@ -236,22 +234,22 @@ struct kvm_arch {
 	 * Otherwise, the guest's EL1 register width has not yet been
 	 * determined yet.
 	 */
-#define KVM_ARCH_FLAG_REG_WIDTH_CONFIGURED		3
-#define KVM_ARCH_FLAG_EL1_32BIT				4
+#define KVM_ARCH_FLAG_REG_WIDTH_CONFIGURED		2
+#define KVM_ARCH_FLAG_EL1_32BIT				3
 	/* PSCI SYSTEM_SUSPEND enabled for the guest */
-#define KVM_ARCH_FLAG_SYSTEM_SUSPEND_ENABLED		5
+#define KVM_ARCH_FLAG_SYSTEM_SUSPEND_ENABLED		4
 	/* VM counter offset */
-#define KVM_ARCH_FLAG_VM_COUNTER_OFFSET			6
+#define KVM_ARCH_FLAG_VM_COUNTER_OFFSET			5
 	/* Timer PPIs made immutable */
-#define KVM_ARCH_FLAG_TIMER_PPIS_IMMUTABLE		7
+#define KVM_ARCH_FLAG_TIMER_PPIS_IMMUTABLE		6
 	/* SMCCC filter initialized for the VM */
-#define KVM_ARCH_FLAG_SMCCC_FILTER_CONFIGURED		8
+#define KVM_ARCH_FLAG_SMCCC_FILTER_CONFIGURED		7
 	/*
 	 * AA64DFR0_EL1.PMUver was set as ID_AA64DFR0_EL1_PMUVer_IMP_DEF
 	 * or DFR0_EL1.PerfMon was set as ID_DFR0_EL1_PerfMon_IMPDEF from
 	 * userspace for VCPUs without PMU.
 	 */
-#define KVM_ARCH_FLAG_VCPU_HAS_IMP_DEF_PMU		9
+#define KVM_ARCH_FLAG_VCPU_HAS_IMP_DEF_PMU		8
 
 	unsigned long flags;
 

@@ -1112,7 +1110,8 @@ bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu);
 
 #define kvm_has_mte(kvm)					\
 	(system_supports_mte() &&				\
-	 test_bit(KVM_ARCH_FLAG_MTE_ENABLED, &(kvm)->arch.flags))
+	 FIELD_GET(ID_AA64PFR1_EL1_MTE_MASK,			\
+		   IDREG(kvm, SYS_ID_AA64PFR1_EL1)))
 
 #define kvm_supports_32bit_el0()				\
 	(system_supports_32bit_el0() &&				\

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index ca18c09ccf82..6fc4190559d1 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c

@@ -80,8 +80,17 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 		if (!system_supports_mte() || kvm->created_vcpus) {
 			r = -EINVAL;
 		} else {
+			u64 val;
+
+			/* Protects the idregs against modification */
+			mutex_lock(&kvm->arch.config_lock);
+
+			val = IDREG(kvm, SYS_ID_AA64PFR1_EL1);
+			val |= FIELD_PREP(ID_AA64PFR1_EL1_MTE_MASK, 1);

+			IDREG(kvm, SYS_ID_AA64PFR1_EL1) = val;
+
+			mutex_unlock(&kvm->arch.config_lock);
 			r = 0;
-			set_bit(KVM_ARCH_FLAG_MTE_ENABLED, &kvm->arch.flags);
 		}
 		mutex_unlock(&kvm->lock);
 		break;

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 59f8adda47fa..8cffb82dd10d 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c

@@ -3672,6 +3672,11 @@ void kvm_arm_init_id_regs(struct kvm *kvm)
 		idreg++;
 		id = reg_to_encoding(idreg);
 	}
+
+	/* MTE disabled by default even when supported */
+	val = IDREG(kvm, SYS_ID_AA64PFR1_EL1);
+	val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_MTE);
+	IDREG(kvm, SYS_ID_AA64PFR1_EL1) = val;
 }
 
 int __init kvm_sys_reg_table_init(void)