| From 21cbe3cc8a48ff17059912e019fbde28ed54745a Mon Sep 17 00:00:00 2001 |
| From: Marc Zyngier <marc.zyngier@arm.com> |
| Date: Tue, 6 Dec 2016 14:34:22 +0000 |
| Subject: arm64: KVM: pmu: Reset PMSELR_EL0.SEL to a sane value before entering the guest |
| |
| From: Marc Zyngier <marc.zyngier@arm.com> |
| |
| commit 21cbe3cc8a48ff17059912e019fbde28ed54745a upstream. |
| |
| The ARMv8 architecture allows the cycle counter to be configured |
| by setting PMSELR_EL0.SEL==0x1f and then accessing PMXEVTYPER_EL0, |
| hence accessing PMCCFILTR_EL0. But it disallows the use of |
| PMSELR_EL0.SEL==0x1f to access the cycle counter itself through |
| PMXEVCNTR_EL0. |
| |
| Linux itself doesn't violate this rule, but we may end up with |
| PMSELR_EL0.SEL being set to 0x1f when we enter a guest. If that |
| guest accesses PMXEVCNTR_EL0, the access may UNDEF at EL1, |
| despite the guest not having done anything wrong. |
| |
| In order to avoid this unfortunate course of events (haha!), let's |
| sanitize PMSELR_EL0 on guest entry. This ensures that the guest |
| won't explode unexpectedly. |
| |
| Acked-by: Will Deacon <will.deacon@arm.com> |
| Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| arch/arm64/kvm/hyp/switch.c | 8 +++++++- |
| 1 file changed, 7 insertions(+), 1 deletion(-) |
| |
| --- a/arch/arm64/kvm/hyp/switch.c |
| +++ b/arch/arm64/kvm/hyp/switch.c |
| @@ -82,7 +82,13 @@ static void __hyp_text __activate_traps( |
| write_sysreg(val, hcr_el2); |
| /* Trap on AArch32 cp15 c15 accesses (EL1 or EL0) */ |
| write_sysreg(1 << 15, hstr_el2); |
| - /* Make sure we trap PMU access from EL0 to EL2 */ |
| + /* |
| + * Make sure we trap PMU access from EL0 to EL2. Also sanitize |
| + * PMSELR_EL0 to make sure it never contains the cycle |
| + * counter, which could make a PMXEVCNTR_EL0 access UNDEF at |
| + * EL1 instead of being trapped to EL2. |
| + */ |
| + write_sysreg(0, pmselr_el0); |
| write_sysreg(ARMV8_PMU_USERENR_MASK, pmuserenr_el0); |
| write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2); |
| __activate_traps_arch()(); |
