[RFC PATCH v2 12/28] KVM: arm64: Make ID_DFR0_EL1 writable

[Reiji Watanabe]

This patch adds id_reg_info for ID_DFR0_EL1 to make it writable
by userspace.

Return an error if userspace tries to set PerfMon field of the
register to a value that conflicts with the PMU configuration.

Signed-off-by: Reiji Watanabe <reijiw at google.com>
---
 arch/arm64/kvm/sys_regs.c | 58 +++++++++++++++++++++++++++++++--------
 1 file changed, 47 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 54bc3641d582..8abd3f6fd667 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -654,6 +654,27 @@ static int validate_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
 	return 0;
 }
 
+static int validate_id_dfr0_el1(struct kvm_vcpu *vcpu,
+				const struct id_reg_info *id_reg, u64 val)
+{
+	bool vcpu_pmu, dfr0_pmu;
+	unsigned int perfmon;
+
+	perfmon = cpuid_feature_extract_unsigned_field(val, ID_DFR0_PERFMON_SHIFT);
+	if (perfmon == 1 || perfmon == 2)
+		/* PMUv1 or PMUv2 is not allowed on ARMv8. */
+		return -EINVAL;
+
+	vcpu_pmu = kvm_vcpu_has_pmu(vcpu);
+	dfr0_pmu = id_reg_has_pmu(val, ID_DFR0_PERFMON_SHIFT, ID_DFR0_PERFMON_8_0);
+
+	/* Check if there is a conflict with a request via KVM_ARM_VCPU_INIT */
+	if (vcpu_pmu ^ dfr0_pmu)
+		return -EPERM;
+
+	return 0;
+}
+
 static void init_id_aa64pfr0_el1_info(struct id_reg_info *id_reg)
 {
 	u64 limit = id_reg->vcpu_limit_val;
@@ -707,6 +728,15 @@ static void init_id_aa64dfr0_el1_info(struct id_reg_info *id_reg)
 	id_reg->vcpu_limit_val = limit;
 }
 
+static void init_id_dfr0_el1_info(struct id_reg_info *id_reg)
+{
+	/* Limit guests to PMUv3 for ARMv8.4 */
+	id_reg->vcpu_limit_val =
+		cpuid_feature_cap_perfmon_field(id_reg->vcpu_limit_val,
+						ID_DFR0_PERFMON_SHIFT,
+						ID_DFR0_PERFMON_8_4);
+}
+
 static u64 get_reset_id_aa64pfr0_el1(struct kvm_vcpu *vcpu,
 				     const struct id_reg_info *idr)
 {
@@ -738,6 +768,14 @@ static u64 get_reset_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
 	       (idr->vcpu_limit_val & ~(ARM64_FEATURE_MASK(ID_AA64DFR0_PMUVER)));
 }
 
+static u64 get_reset_id_dfr0_el1(struct kvm_vcpu *vcpu,
+				 const struct id_reg_info *idr)
+{
+	return kvm_vcpu_has_pmu(vcpu) ?
+	       idr->vcpu_limit_val :
+	       (idr->vcpu_limit_val & ~(ARM64_FEATURE_MASK(ID_DFR0_PERFMON)));
+}
+
 static struct id_reg_info id_aa64pfr0_el1_info = {
 	.sys_reg = SYS_ID_AA64PFR0_EL1,
 	.ftr_check_types = S_FCT(ID_AA64PFR0_ASIMD_SHIFT, FCT_LOWER_SAFE) |
@@ -790,6 +828,13 @@ static struct id_reg_info id_aa64dfr0_el1_info = {
 	.get_reset_val = get_reset_id_aa64dfr0_el1,
 };
 
+static struct id_reg_info id_dfr0_el1_info = {
+	.sys_reg = SYS_ID_DFR0_EL1,
+	.init = init_id_dfr0_el1_info,
+	.validate = validate_id_dfr0_el1,
+	.get_reset_val = get_reset_id_dfr0_el1,
+};
+
 /*
  * An ID register that needs special handling to control the value for the
  * guest must have its own id_reg_info in id_reg_info_table.
@@ -799,6 +844,7 @@ static struct id_reg_info id_aa64dfr0_el1_info = {
  */
 #define	GET_ID_REG_INFO(id)	(id_reg_info_table[IDREG_IDX(id)])
 static struct id_reg_info *id_reg_info_table[KVM_ARM_ID_REG_MAX_NUM] = {
+	[IDREG_IDX(SYS_ID_DFR0_EL1)] = &id_dfr0_el1_info,
 	[IDREG_IDX(SYS_ID_AA64PFR0_EL1)] = &id_aa64pfr0_el1_info,
 	[IDREG_IDX(SYS_ID_AA64PFR1_EL1)] = &id_aa64pfr1_el1_info,
 	[IDREG_IDX(SYS_ID_AA64DFR0_EL1)] = &id_aa64dfr0_el1_info,
@@ -1636,18 +1682,8 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
 		struct sys_reg_desc const *r, bool raz)
 {
 	u32 id = reg_to_encoding(r);
-	u64 val = raz ? 0 : __vcpu_sys_reg(vcpu, IDREG_SYS_IDX(id));
-
-	switch (id) {
-	case SYS_ID_DFR0_EL1:
-		/* Limit guests to PMUv3 for ARMv8.4 */
-		val = cpuid_feature_cap_perfmon_field(val,
-						      ID_DFR0_PERFMON_SHIFT,
-						      kvm_vcpu_has_pmu(vcpu) ? ID_DFR0_PERFMON_8_4 : 0);
-		break;
-	}
 
-	return val;
+	return raz ? 0 : __vcpu_sys_reg(vcpu, IDREG_SYS_IDX(id));
 }
 
 static unsigned int id_visibility(const struct kvm_vcpu *vcpu,
-- 
2.33.1.1089.g2158813163f-goog