linux-kernel - [PATCH v2 17/23] KVM: arm64: Account for partitioning in PMCR

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Message-ID: <20250620221326.1261128-19-coltonlewis@google.com>
Date: Fri, 20 Jun 2025 22:13:18 +0000
From: Colton Lewis <coltonlewis@...gle.com>
To: kvm@...r.kernel.org
Cc: Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>, 
	Russell King <linux@...linux.org.uk>, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
	Joey Gouly <joey.gouly@....com>, Suzuki K Poulose <suzuki.poulose@....com>, 
	Zenghui Yu <yuzenghui@...wei.com>, Mark Rutland <mark.rutland@....com>, 
	Shuah Khan <shuah@...nel.org>, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
	linux-perf-users@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	Colton Lewis <coltonlewis@...gle.com>
Subject: [PATCH v2 17/23] KVM: arm64: Account for partitioning in PMCR_EL0 access

For some reason unknown to me, KVM allows writes to PMCR_EL0.N even
though the architecture specifies that field as RO. Make sure these
accesses conform to additional constraints imposed when the PMU is
partitioned.

Signed-off-by: Colton Lewis <coltonlewis@...gle.com>
---
 arch/arm64/kvm/pmu.c      | 2 +-
 arch/arm64/kvm/sys_regs.c | 4 +++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/pmu.c b/arch/arm64/kvm/pmu.c
index 90fc088ce3d3..5f0847dc7d53 100644
--- a/arch/arm64/kvm/pmu.c
+++ b/arch/arm64/kvm/pmu.c
@@ -884,7 +884,7 @@ u64 kvm_pmu_accessible_counter_mask(struct kvm_vcpu *vcpu)
 u64 kvm_vcpu_read_pmcr(struct kvm_vcpu *vcpu)
 {
 	u64 pmcr = __vcpu_sys_reg(vcpu, PMCR_EL0);
-	u64 n = kvm_pmu_hpmn(vcpu);
+	u64 n = kvm_pmu_guest_num_counters(vcpu);
 
 	if (vcpu_has_nv(vcpu) && !vcpu_is_el2(vcpu))
 		n = FIELD_GET(MDCR_EL2_HPMN, __vcpu_sys_reg(vcpu, MDCR_EL2));
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 1ea7d092ec59..b64b60e297bd 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1266,7 +1266,9 @@ static int set_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r,
 	 */
 	if (!kvm_vm_has_ran_once(kvm) &&
 	    !vcpu_has_nv(vcpu)	      &&
-	    new_n <= kvm_arm_pmu_get_max_counters(kvm))
+	    new_n <= kvm_arm_pmu_get_max_counters(kvm) &&
+	    (!kvm_vcpu_pmu_is_partitioned(vcpu) ||
+	     new_n <= kvm->arch.arm_pmu->hpmn_max))
 		kvm->arch.nr_pmu_counters = new_n;
 
 	mutex_unlock(&kvm->arch.config_lock);
-- 
2.50.0.714.g196bf9f422-goog