[PATCH v3 4/6] KVM: arm64: PMU: Reload when user modifies registers

[Akihiko Odaki]

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

Signed-off-by: Akihiko Odaki <akihiko.odaki at daynix.com>
---
 arch/arm64/kvm/pmu-emul.c | 3 ---
 arch/arm64/kvm/sys_regs.c | 6 ++++++
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 1cfe53b6353e..78cfa8b0964d 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -862,9 +862,6 @@ 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 26182cae4ac7..307ce37d0434 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1143,6 +1143,7 @@ static bool access_pmu_evtyper(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
 static int set_pmreg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r, u64 val)
 {
 	__vcpu_sys_reg(vcpu, r->reg) = val & kvm_pmu_valid_counter_mask(vcpu);
+	kvm_make_request(KVM_REQ_RELOAD_PMU, vcpu);
 	return 0;
 }
 
@@ -1303,6 +1304,8 @@ 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;
 }
 
@@ -4259,6 +4262,9 @@ void kvm_reset_sys_regs(struct kvm_vcpu *vcpu)
 	}
 
 	set_bit(KVM_ARCH_FLAG_ID_REGS_INITIALIZED, &kvm->arch.flags);
+
+	if (kvm_vcpu_has_pmu(vcpu))
+		kvm_make_request(KVM_REQ_RELOAD_PMU, vcpu);
 }
 
 /**

-- 
2.48.1