KVM: arm64: PMU: Reload when user modifies registers

Commit d0c94c49792c ("KVM: arm64: Restore PMU configuration on first
run") added the code to reload the PMU configuration on first run.

It is also important to keep the correct state even if system registers
are modified after first run, specifically when debugging Windows on
QEMU with GDB; QEMU tries to write back all visible registers when
resuming the VM execution with GDB, corrupting the PMU state. Windows
always uses the PMU so this can cause adverse effects on that particular
OS.

The usual register writes and reset are already handled independently,
but register writes from userspace are not covered.
Trigger the code to reload the PMU configuration for them instead so
that PMU configuration changes made by users will be applied also after
the first run.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250315-pmc-v5-4-ecee87dab216@daynix.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 593216bc14f0dcf4ddbeb80f16b269a9b03f7dd2..8e10124a7420f5a1a601303f281cb3f107309108 100644 (file)
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -917,9 +917,6 @@ int kvm_arm_pmu_v3_enable(struct kvm_vcpu *vcpu)
                   return -EINVAL;
        }
 
-       /* One-off reload of the PMU on first run */
-       kvm_make_request(KVM_REQ_RELOAD_PMU, vcpu);
-
        return 0;
 }
 

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 4d1ef47d00495fc6307e94a5a2f649c4228fbd79..727579acc7f6007e7afc5e14f0050a850f31abc1 100644 (file)
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1070,6 +1070,8 @@ static int set_pmreg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r, u64 va
        u64 mask = kvm_pmu_accessible_counter_mask(vcpu);
 
        __vcpu_sys_reg(vcpu, r->reg) = val & mask;
+       kvm_make_request(KVM_REQ_RELOAD_PMU, vcpu);
+
        return 0;
 }
 
@@ -1228,6 +1230,8 @@ static int set_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r,
                val |= ARMV8_PMU_PMCR_LC;
 
        __vcpu_sys_reg(vcpu, r->reg) = val;
+       kvm_make_request(KVM_REQ_RELOAD_PMU, vcpu);
+
        return 0;
 }