Commit 1db4aaa0 authored Mar 15, 2025 by Akihiko Odaki Committed by Oliver Upton Mar 17, 2025

KVM: arm64: PMU: Reload when user modifies registers



Commit d0c94c49 ("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>

parent 64074ca8

arch/arm64/kvm/pmu-emul.c

+0 −3

Original line number	Diff line number	Diff line
		@@ -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;
		}

arch/arm64/kvm/sys_regs.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -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;
		}