Re: [PATCH v2 11/18] KVM: arm64: don't trap Statistical Profiling controls to EL2

Mark Rutland
2019-12-20T18:08:21Z

On Fri, Dec 20, 2019 at 02:30:18PM +0000, Andrew Murray wrote:
> As we now save/restore the profiler state there is no need to trap
> accesses to the statistical profiling controls. Let's unset the
> _TPMS bit.
>
> Signed-off-by: Andrew Murray <andrew.murray@arm.com>
> ---
> arch/arm64/kvm/debug.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
> index 43487f035385..07ca783e7d9e 100644
> --- a/arch/arm64/kvm/debug.c
> +++ b/arch/arm64/kvm/debug.c
> @@ -88,7 +88,6 @@ void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu)
> * - Performance monitors (MDCR_EL2_TPM/MDCR_EL2_TPMCR)
> * - Debug ROM Address (MDCR_EL2_TDRA)
> * - OS related registers (MDCR_EL2_TDOSA)
> - * - Statistical profiler (MDCR_EL2_TPMS/MDCR_EL2_E2PB)
> *
> * Additionally, KVM only traps guest accesses to the debug registers if
> * the guest is not actively using them (see the KVM_ARM64_DEBUG_DIRTY
> @@ -111,7 +110,6 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
> */
> vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK;
> vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
> - MDCR_EL2_TPMS |
> MDCR_EL2_TPMCR |
> MDCR_EL2_TDRA |
> MDCR_EL2_TDOSA);

I think that this should be conditional on some vcpu feature flag.

If nothing else, this could break existing migration cases otherwise.

Thanks,
Mark.