[PATCH v3 3/4] KVM: arm64: Enable writable for ID_AA64PFR0_EL1

[Jing Zhang]

Return an error if userspace tries to set SVE field of the register
to a value that conflicts with SVE configuration for the guest.
SIMD/FP/SVE fields of the requested value are validated according to
Arm ARM.

Signed-off-by: Jing Zhang <jingzhangos at google.com>
---
 arch/arm64/kvm/id_regs.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/id_regs.c b/arch/arm64/kvm/id_regs.c
index 11d3a1d46ee5..20d1a2d2a0cc 100644
--- a/arch/arm64/kvm/id_regs.c
+++ b/arch/arm64/kvm/id_regs.c
@@ -283,6 +283,9 @@ static u64 read_sanitised_id_aa64pfr0_el1(struct kvm_vcpu *vcpu,
 
 	val &= ~ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_AMU);
 
+	if (!system_supports_sve())
+		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_SVE);
+
 	return val;
 }
 
@@ -291,6 +294,22 @@ static int set_id_aa64pfr0_el1(struct kvm_vcpu *vcpu,
 			       u64 val)
 {
 	u8 csv2, csv3;
+	int fp, simd;
+	bool has_sve = id_aa64pfr0_sve(val);
+
+	simd = cpuid_feature_extract_signed_field(val, ID_AA64PFR0_EL1_AdvSIMD_SHIFT);
+	fp = cpuid_feature_extract_signed_field(val, ID_AA64PFR0_EL1_FP_SHIFT);
+	/* AdvSIMD field must have the same value as FP field */
+	if (simd != fp)
+		return -EINVAL;
+
+	/* fp must be supported when sve is supported */
+	if (has_sve && (fp < 0))
+		return -EINVAL;
+
+	/* Check if there is a conflict with a request via KVM_ARM_VCPU_INIT */
+	if (vcpu_has_sve(vcpu) ^ has_sve)
+		return -EPERM;
 
 	/*
 	 * Allow AA64PFR0_EL1.CSV2 to be set from userspace as long as
@@ -582,7 +601,7 @@ const struct sys_reg_desc id_reg_descs[KVM_ARM_ID_REG_NUM] = {
 	  .get_user = get_id_reg,
 	  .set_user = set_id_aa64pfr0_el1,
 	  .reset = read_sanitised_id_aa64pfr0_el1,
-	  .val = ID_AA64PFR0_EL1_CSV2_MASK | ID_AA64PFR0_EL1_CSV3_MASK, },
+	  .val = GENMASK(63, 0), },
 	ID_SANITISED(ID_AA64PFR1_EL1),
 	ID_UNALLOCATED(4, 2),
 	ID_UNALLOCATED(4, 3),
-- 
2.40.0.348.gf938b09366-goog