[PATCH v2 11/14] KVM: arm64: PMU: Allow ID_AA64DFR0_EL1.PMUver to be set from userspace

[Marc Zyngier <maz@kernel.org>]

Allow userspace to write ID_AA64DFR0_EL1, on the condition that only
the PMUver field can be altered and be at most the one that was
initially computed for the guest.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/kvm/sys_regs.c | 37 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 7a4cd644b9c0..4fa14b4ae2a6 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1247,6 +1247,40 @@ static int set_id_aa64pfr0_el1(struct kvm_vcpu *vcpu,
 	return 0;
 }
 
+static int set_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
+			       const struct sys_reg_desc *rd,
+			       u64 val)
+{
+	u8 pmuver, host_pmuver;
+
+	host_pmuver = kvm_arm_pmu_get_pmuver_limit();
+
+	/*
+	 * Allow AA64DFR0_EL1.PMUver to be set from userspace as long
+	 * as it doesn't promise more than what the HW gives us. We
+	 * allow an IMPDEF PMU though, only if no PMU is supported
+	 * (KVM backward compatibility handling).
+	 */
+	pmuver = FIELD_GET(ARM64_FEATURE_MASK(ID_AA64DFR0_EL1_PMUVer), val);
+	if (pmuver != ID_AA64DFR0_EL1_PMUVer_IMP_DEF && pmuver > host_pmuver)
+		return -EINVAL;
+
+	/* We already have a PMU, don't try to disable it... */
+	if (kvm_vcpu_has_pmu(vcpu) &&
+	    (pmuver == 0 || pmuver == ID_AA64DFR0_EL1_PMUVer_IMP_DEF))
+		return -EINVAL;
+
+	/* 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;
+
+	vcpu->kvm->arch.dfr0_pmuver = pmuver;
+
+	return 0;
+}
+
 /*
  * cpufeature ID register user accessors
  *
@@ -1508,7 +1542,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	ID_UNALLOCATED(4,7),
 
 	/* CRm=5 */
-	ID_SANITISED(ID_AA64DFR0_EL1),
+	{ SYS_DESC(SYS_ID_AA64DFR0_EL1), .access = access_id_reg,
+	  .get_user = get_id_reg, .set_user = set_id_aa64dfr0_el1, },
 	ID_SANITISED(ID_AA64DFR1_EL1),
 	ID_UNALLOCATED(5,2),
 	ID_UNALLOCATED(5,3),
-- 
2.34.1


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