From 6d4f9236cd678e0bf0c09fd0e1fa20435bb2e5a2 Mon Sep 17 00:00:00 2001 From: Oliver Upton Date: Thu, 13 Jul 2023 22:16:49 +0000 Subject: [PATCH] KVM: arm64: Correctly handle RES0 bits PMEVTYPER_EL0.evtCount The PMU event ID varies from 10 to 16 bits, depending on the PMU version. If the PMU only supports 10 bits of event ID, bits [15:10] of the evtCount field behave as RES0. While the actual PMU emulation code gets this right (i.e. RES0 bits are masked out when programming the perf event), the sysreg emulation writes an unmasked value to the in-memory cpu context. The net effect is that guest reads and writes of PMEVTYPER_EL0 will see non-RES0 behavior in the reserved bits of the field. As it so happens, kvm_pmu_set_counter_event_type() already writes a masked value to the in-memory context that gets overwritten by access_pmu_evtyper(). Fix the issue by removing the unnecessary (and incorrect) register write in access_pmu_evtyper(). Reviewed-by: Marc Zyngier Reviewed-by: Reiji Watanabe Link: https://lore.kernel.org/r/20230713221649.3889210-1-oliver.upton@linux.dev Signed-off-by: Oliver Upton --- arch/arm64/kvm/sys_regs.c | 1 - 1 file changed, 1 deletion(-) diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c index bd3431823ec5..fa7597882ed8 100644 --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c @@ -986,7 +986,6 @@ static bool access_pmu_evtyper(struct kvm_vcpu *vcpu, struct sys_reg_params *p, if (p->is_write) { kvm_pmu_set_counter_event_type(vcpu, p->regval, idx); - __vcpu_sys_reg(vcpu, reg) = p->regval & ARMV8_PMU_EVTYPE_MASK; kvm_vcpu_pmu_restore_guest(vcpu); } else { p->regval = __vcpu_sys_reg(vcpu, reg) & ARMV8_PMU_EVTYPE_MASK;