On Tue, 28 Mar 2023 04:47:25 +0100,
Reiji Watanabe <reijiw@xxxxxxxxxx> wrote:
>
> Currently, with VHE, KVM enables the EL0 event counting for the
> guest on vcpu_load() or KVM enables it as a part of the PMU
> register emulation process, when needed. However, in the migration
> case (with VHE), the same handling is lacking. So, enable it on the
> first KVM_RUN with VHE (after the migration) when needed.
It wasn't completely clear to me how the migration case was affected
by this until I started digging into the call stack:
At load-time, the PMCR_EL0 effects haven't been propagated yet (the
events haven't been created, as this is what kvm_pmu_handle_pmcr()
does on first run). So there is an ordering inversion between
kvm_pmu_handle_pmcr() and kvm_vcpu_pmu_restore_guest().
Moving the latter call into the former fixes the issue, completely
emulating an extra write to PMCR_EL0.
I think it would be worth capturing some of the above in the commit
message so that it doesn't get lost...
>
> Fixes: d0c94c49792c ("KVM: arm64: Restore PMU configuration on first run")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Reiji Watanabe <reijiw@xxxxxxxxxx>
> ---
> arch/arm64/kvm/pmu-emul.c | 1 +
> arch/arm64/kvm/sys_regs.c | 1 -
> 2 files changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
> index c243b10f3e15..5eca0cdd961d 100644
> --- a/arch/arm64/kvm/pmu-emul.c
> +++ b/arch/arm64/kvm/pmu-emul.c
> @@ -558,6 +558,7 @@ void kvm_pmu_handle_pmcr(struct kvm_vcpu *vcpu, u64 val)
> for_each_set_bit(i, &mask, 32)
> kvm_pmu_set_pmc_value(kvm_vcpu_idx_to_pmc(vcpu, i), 0, true);
> }
> + kvm_vcpu_pmu_restore_guest(vcpu);
> }
>
> static bool kvm_pmu_counter_is_enabled(struct kvm_pmc *pmc)
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 1b2c161120be..34688918c811 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -794,7 +794,6 @@ static bool access_pmcr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
> if (!kvm_supports_32bit_el0())
> val |= ARMV8_PMU_PMCR_LC;
> kvm_pmu_handle_pmcr(vcpu, val);
> - kvm_vcpu_pmu_restore_guest(vcpu);
> } else {
> /* PMCR.P & PMCR.C are RAZ */
> val = __vcpu_sys_reg(vcpu, PMCR_EL0)
With the nitpicking above addressed, and should this go into 6.3 as a
fix:
Reviewed-by: Marc Zyngier <maz@xxxxxxxxxx>
I can otherwise take it into 6.4, depending on what Oliver decides to
do.
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
