[PATCH v2 1/2] KVM: arm64: Enable writable for ID_AA64DFR0_EL1

[Jing Zhang]

Since number of context-aware breakpoints must be no more than number
of supported breakpoints according to Arm ARM, return an error if
userspace tries to set CTX_CMPS field to such value.

Signed-off-by: Jing Zhang <jingzhangos at google.com>
---
 arch/arm64/kvm/id_regs.c | 43 ++++++++++++++++++++++------------------
 1 file changed, 24 insertions(+), 19 deletions(-)

diff --git a/arch/arm64/kvm/id_regs.c b/arch/arm64/kvm/id_regs.c
index 395eaf84a0ab..7ca76a167c90 100644
--- a/arch/arm64/kvm/id_regs.c
+++ b/arch/arm64/kvm/id_regs.c
@@ -355,10 +355,15 @@ static int set_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
 			       const struct sys_reg_desc *rd,
 			       u64 val)
 {
-	u8 pmuver, host_pmuver;
+	u8 pmuver, host_pmuver, brps, ctx_cmps;
 	bool valid_pmu;
 	int ret;
 
+	brps = FIELD_GET(ARM64_FEATURE_MASK(ID_AA64DFR0_EL1_BRPs), val);
+	ctx_cmps = FIELD_GET(ARM64_FEATURE_MASK(ID_AA64DFR0_EL1_CTX_CMPs), val);
+	if (ctx_cmps > brps)
+		return -EINVAL;
+
 	host_pmuver = kvm_arm_pmu_get_pmuver_limit();
 
 	/*
@@ -377,28 +382,28 @@ static int set_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
 	if (kvm_vcpu_has_pmu(vcpu) != valid_pmu)
 		return -EINVAL;
 
-	if (valid_pmu) {
-		mutex_lock(&vcpu->kvm->arch.config_lock);
-		ret = set_id_reg(vcpu, rd, val);
-		if (ret) {
-			mutex_unlock(&vcpu->kvm->arch.config_lock);
-			return ret;
-		}
+	if (!valid_pmu) {
+		/* Igore the pmuver field in val */
+		pmuver = FIELD_GET(ID_AA64DFR0_EL1_PMUVer_MASK, read_id_reg(vcpu, rd));
+		val &= ~ID_AA64DFR0_EL1_PMUVer_MASK;
+		val |= FIELD_PREP(ID_AA64DFR0_EL1_PMUVer_MASK, pmuver);
+	}
 
-		IDREG(vcpu->kvm, SYS_ID_DFR0_EL1) &= ~ARM64_FEATURE_MASK(ID_DFR0_EL1_PerfMon);
-		IDREG(vcpu->kvm, SYS_ID_DFR0_EL1) |=
-			FIELD_PREP(ARM64_FEATURE_MASK(ID_DFR0_EL1_PerfMon), pmuver_to_perfmon(pmuver));
+	mutex_lock(&vcpu->kvm->arch.config_lock);
+	ret = set_id_reg(vcpu, rd, val);
+	if (ret) {
 		mutex_unlock(&vcpu->kvm->arch.config_lock);
-	} else {
-		/* We can only differ with PMUver, and anything else is an error */
-		val ^= read_id_reg(vcpu, rd);
-		val &= ~ARM64_FEATURE_MASK(ID_AA64DFR0_EL1_PMUVer);
-		if (val)
-			return -EINVAL;
+		return ret;
+	}
 
+	IDREG(vcpu->kvm, SYS_ID_DFR0_EL1) &= ~ARM64_FEATURE_MASK(ID_DFR0_EL1_PerfMon);
+	IDREG(vcpu->kvm, SYS_ID_DFR0_EL1) |=
+		FIELD_PREP(ARM64_FEATURE_MASK(ID_DFR0_EL1_PerfMon), pmuver_to_perfmon(pmuver));
+
+	if (!valid_pmu)
 		assign_bit(KVM_ARCH_FLAG_VCPU_HAS_IMP_DEF_PMU, &vcpu->kvm->arch.flags,
 			   pmuver == ID_AA64DFR0_EL1_PMUVer_IMP_DEF);
-	}
+	mutex_unlock(&vcpu->kvm->arch.config_lock);
 
 	return 0;
 }
@@ -610,7 +615,7 @@ static struct id_reg_desc id_reg_descs[KVM_ARM_ID_REG_NUM] = {
 		.get_user = get_id_reg,
 		.set_user = set_id_aa64dfr0_el1, },
 	  .ftr_bits = ftr_id_aa64dfr0,
-	  .writable_mask = ID_AA64DFR0_EL1_PMUVer_MASK,
+	  .writable_mask = GENMASK(63, 0),
 	  .read_kvm_sanitised_reg = read_sanitised_id_aa64dfr0_el1,
 	},
 	ID_SANITISED(ID_AA64DFR1_EL1),
-- 
2.40.0.348.gf938b09366-goog