[PATCH 1/7] KVM: arm64: PMU: Have reset_pmu_reg() to clear a register

[Reiji Watanabe]

On vCPU reset, PMCNTEN{SET,CLR}_EL1 and PMOVS{SET,CLR}_EL1 for
a vCPU are reset by reset_pmu_reg(). This function clears RAZ bits
of those registers corresponding to unimplemented event counters
on the vCPU, and sets bits corresponding to implemented event counters
to a predefined pseudo UNKNOWN value (some bits are set to 1).

The function identifies (un)implemented event counters on the
vCPU based on the PMCR_EL1.N value on the host. Using the host
value for this would be problematic when KVM supports letting
userspace set PMCR_EL1.N to a value different from the host value
(some of the RAZ bits of those registers could end up being set to 1).

Fix reset_pmu_reg() to clear the registers so that it can ensure
that all the RAZ bits are cleared even when the PMCR_EL1.N value
for the vCPU is different from the host value.

Signed-off-by: Reiji Watanabe <reijiw at google.com>
---
 arch/arm64/kvm/sys_regs.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index c6cbfe6b854b..ec4bdaf71a15 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -604,19 +604,11 @@ static unsigned int pmu_visibility(const struct kvm_vcpu *vcpu,
 
 static void reset_pmu_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
 {
-	u64 n, mask = BIT(ARMV8_PMU_CYCLE_IDX);
-
 	/* No PMU available, any PMU reg may UNDEF... */
 	if (!kvm_arm_support_pmu_v3())
 		return;
 
-	n = read_sysreg(pmcr_el0) >> ARMV8_PMU_PMCR_N_SHIFT;
-	n &= ARMV8_PMU_PMCR_N_MASK;
-	if (n)
-		mask |= GENMASK(n - 1, 0);
-
-	reset_unknown(vcpu, r);
-	__vcpu_sys_reg(vcpu, r->reg) &= mask;
+	__vcpu_sys_reg(vcpu, r->reg) = 0;
 }
 
 static void reset_pmevcntr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
-- 
2.39.0.314.g84b9a713c41-goog