[v2,3/3] KVM: arm64: PMU: Set raw values from user to PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}

Commit Message

Akihiko Odaki March 7, 2025, 10:55 a.m. UTC

Commit a45f41d754e0 ("KVM: arm64: Add {get,set}_user for
PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}") changed KVM_SET_ONE_REG to update
the mentioned registers in a way matching with the behavior of guest
register writes. This is a breaking change of a UAPI though the new
semantics looks cleaner and VMMs are not prepared for this.

Firecracker, QEMU, and crosvm perform migration by listing registers
with KVM_GET_REG_LIST, getting their values with KVM_GET_ONE_REG and
setting them with KVM_SET_ONE_REG. This algorithm assumes
KVM_SET_ONE_REG restores the values retrieved with KVM_GET_ONE_REG
without any alteration. However, bit operations added by the earlier
commit do not preserve the values retried with KVM_GET_ONE_REG and
potentially break migration.

Remove the bit operations that alter the values retrieved with
KVM_GET_ONE_REG.

Fixes: a45f41d754e0 ("KVM: arm64: Add {get,set}_user for PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}")
Signed-off-by: Akihiko Odaki <[e-mail]>
---
 arch/arm64/kvm/sys_regs.c | 21 +--------------------
 1 file changed, 1 insertion(+), 20 deletions(-)

Patch

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 51054b7befc0b4bd822cecf717ee4a4740c4a685..2f44d4d4f54112787683dd75ea93fd60e92dd31f 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1142,26 +1142,7 @@  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)
 {
-	bool set;
-
-	val &= kvm_pmu_valid_counter_mask(vcpu);
-
-	switch (r->reg) {
-	case PMOVSSET_EL0:
-		/* CRm[1] being set indicates a SET register, and CLR otherwise */
-		set = r->CRm & 2;
-		break;
-	default:
-		/* Op2[0] being set indicates a SET register, and CLR otherwise */
-		set = r->Op2 & 1;
-		break;
-	}
-
-	if (set)
-		__vcpu_sys_reg(vcpu, r->reg) |= val;
-	else
-		__vcpu_sys_reg(vcpu, r->reg) &= ~val;
-
+	__vcpu_sys_reg(vcpu, r->reg) = val & kvm_pmu_valid_counter_mask(vcpu);
 	kvm_make_request(KVM_REQ_RELOAD_PMU, vcpu);
 
 	return 0;