[RFC PATCH 10/25] KVM: arm64: Make ID_AA64DFR0_EL1 writable

[Reiji Watanabe]

This patch adds id_reg_info for ID_AA64DFR0_EL1 to make it writable
by userspace.

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

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: Reiji Watanabe <reijiw at google.com>
---
 arch/arm64/kvm/sys_regs.c | 108 ++++++++++++++++++++++++++++++++++----
 1 file changed, 97 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 7819a07ee248..61e61f4bb81c 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -402,6 +402,46 @@ static int validate_id_aa64isar1_el1(struct kvm_vcpu *vcpu, u64 val)
 	return 0;
 }
 
+static bool id_reg_has_pmu(u64 val, u64 shift, u64 min)
+{
+	u64 pmu = ((val >> shift) & 0xf);
+
+	/*
+	 * Treat IMPLEMENTATION DEFINED functionality as unimplemented for
+	 * ID_AA64DFR0_EL1.PMUVer/ID_DFR0_EL1.PerfMon.
+	 */
+	if (pmu == 0xf)
+		pmu = 0;
+
+	return (pmu >= min);
+}
+
+static int validate_id_aa64dfr0_el1(struct kvm_vcpu *vcpu, u64 val)
+{
+	unsigned int brps, ctx_cmps;
+	bool vcpu_pmu = kvm_vcpu_has_pmu(vcpu);
+	bool dfr0_pmu = id_reg_has_pmu(val, ID_AA64DFR0_PMUVER_SHIFT,
+				       ID_AA64DFR0_PMUVER_8_0);
+
+	brps = cpuid_feature_extract_unsigned_field(val,
+						ID_AA64DFR0_BRPS_SHIFT);
+	ctx_cmps = cpuid_feature_extract_unsigned_field(val,
+						ID_AA64DFR0_CTX_CMPS_SHIFT);
+
+	/*
+	 * Number of context-aware breakpoints can be no more than number of
+	 * supported breakpoints.
+	 */
+	if (ctx_cmps > brps)
+		return -EINVAL;
+
+	/* 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;
@@ -445,6 +485,47 @@ static void init_id_aa64isar1_el1_info(struct id_reg_info *id_reg)
 				 (id_reg->sys_val & ~PTRAUTH_MASK);
 }
 
+/*
+ * ID_AA64DFR0_EL1.PMUVer/ID_DFR0_EL1.PerfMon == 0xf indicates
+ * IMPLEMENTATION DEFINED form of performance monitors supported,
+ * PMUv3 not supported (NOTE: 0x0 indicates PMU is not supported).
+ * This function is to cap a value of those two fields with the
+ * given 'cap_val' treating 0xf in the fields as 0.
+ */
+static u64 id_reg_cap_pmu(u64 val, u64 shift, u64 cap_val)
+{
+	u64 mask = 0xf;
+	u64 pmu;
+
+	pmu = (val >> shift) & mask;
+	pmu = (pmu == 0xf) ? 0 : pmu;
+	pmu = min(pmu, cap_val);
+
+	val &= ~(0xfULL << shift);
+	val |= (pmu & 0xf) << shift;
+	return val;
+}
+
+static void init_id_aa64dfr0_el1_info(struct id_reg_info *id_reg)
+{
+	u64 limit;
+
+	id_reg->sys_val = read_sanitised_ftr_reg(id_reg->sys_reg);
+	limit = id_reg->sys_val;
+
+	/* Limit guests to PMUv3 for ARMv8.4 */
+	limit = id_reg_cap_pmu(limit, ID_AA64DFR0_PMUVER_SHIFT,
+			       ID_AA64DFR0_PMUVER_8_4);
+	/* Limit debug to ARMv8.0 */
+	limit &= ~ARM64_FEATURE_MASK(ID_AA64DFR0_DEBUGVER);
+	limit |= (FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64DFR0_DEBUGVER), 6));
+
+	/* Hide SPE from guests */
+	limit &= ~ARM64_FEATURE_MASK(ID_AA64DFR0_PMSVER);
+
+	id_reg->vcpu_limit_val = limit;
+}
+
 static u64 get_reset_id_aa64pfr0_el1(struct kvm_vcpu *vcpu,
 				     struct id_reg_info *idr)
 {
@@ -468,6 +549,14 @@ static u64 get_reset_id_aa64isar1_el1(struct kvm_vcpu *vcpu,
 	       idr->vcpu_limit_val : (idr->vcpu_limit_val & ~PTRAUTH_MASK);
 }
 
+static u64 get_reset_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
+				     struct id_reg_info *idr)
+{
+	return kvm_vcpu_has_pmu(vcpu) ?
+	       idr->vcpu_limit_val :
+	       (idr->vcpu_limit_val & ~(ARM64_FEATURE_MASK(ID_AA64DFR0_PMUVER)));
+}
+
 static struct id_reg_info id_aa64pfr0_el1_info = {
 	.sys_reg = SYS_ID_AA64PFR0_EL1,
 	.init = init_id_aa64pfr0_el1_info,
@@ -497,6 +586,13 @@ static struct id_reg_info id_aa64isar1_el1_info = {
 	.get_reset_val = get_reset_id_aa64isar1_el1,
 };
 
+static struct id_reg_info id_aa64dfr0_el1_info = {
+	.sys_reg = SYS_ID_AA64DFR0_EL1,
+	.init = init_id_aa64dfr0_el1_info,
+	.validate = validate_id_aa64dfr0_el1,
+	.get_reset_val = get_reset_id_aa64dfr0_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.
@@ -508,6 +604,7 @@ static struct id_reg_info id_aa64isar1_el1_info = {
 static struct id_reg_info *id_reg_info_table[KVM_ARM_ID_REG_MAX_NUM] = {
 	[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,
 	[IDREG_IDX(SYS_ID_AA64ISAR0_EL1)] = &id_aa64isar0_el1_info,
 	[IDREG_IDX(SYS_ID_AA64ISAR1_EL1)] = &id_aa64isar1_el1_info,
 };
@@ -1346,17 +1443,6 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu,
 	u64 val = raz ? 0 : __vcpu_sys_reg(vcpu, IDREG_SYS_IDX(id));
 
 	switch (id) {
-	case SYS_ID_AA64DFR0_EL1:
-		/* Limit debug to ARMv8.0 */
-		val &= ~ARM64_FEATURE_MASK(ID_AA64DFR0_DEBUGVER);
-		val |= FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64DFR0_DEBUGVER), 6);
-		/* Limit guests to PMUv3 for ARMv8.4 */
-		val = cpuid_feature_cap_perfmon_field(val,
-						      ID_AA64DFR0_PMUVER_SHIFT,
-						      kvm_vcpu_has_pmu(vcpu) ? ID_AA64DFR0_PMUVER_8_4 : 0);
-		/* Hide SPE from guests */
-		val &= ~ARM64_FEATURE_MASK(ID_AA64DFR0_PMSVER);
-		break;
 	case SYS_ID_DFR0_EL1:
 		/* Limit guests to PMUv3 for ARMv8.4 */
 		val = cpuid_feature_cap_perfmon_field(val,
-- 
2.33.0.882.g93a45727a2-goog