Re: [PATCH RFC V3 25/29] target/arm/kvm: Write CPU state back to KVM on reset

["Nicholas Piggin" <npiggin@gmail.com>]

On Fri Jun 14, 2024 at 9:36 AM AEST, Salil Mehta wrote:
> From: Jean-Philippe Brucker <jean-philippe@linaro.org>
>
> When a KVM vCPU is reset following a PSCI CPU_ON call, its power state
> is not synchronized with KVM at the moment. Because the vCPU is not
> marked dirty, we miss the call to kvm_arch_put_registers() that writes
> to KVM's MP_STATE. Force mp_state synchronization.

Hmm. Is this a bug fix for upstream? arm does respond to CPU_ON calls
by the look, but maybe it's not doing KVM parking until your series?
Maybe just a slight change to say "When KVM parking is implemented for
ARM..." if so.

>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> ---
>  target/arm/kvm.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> index 1121771c4a..7acd83ce64 100644
> --- a/target/arm/kvm.c
> +++ b/target/arm/kvm.c
> @@ -980,6 +980,7 @@ void kvm_arm_cpu_post_load(ARMCPU *cpu)
>  void kvm_arm_reset_vcpu(ARMCPU *cpu)
>  {
>      int ret;
> +    CPUState *cs = CPU(cpu);
>  
>      /* Re-init VCPU so that all registers are set to
>       * their respective reset values.
> @@ -1001,6 +1002,12 @@ void kvm_arm_reset_vcpu(ARMCPU *cpu)
>       * for the same reason we do so in kvm_arch_get_registers().
>       */
>      write_list_to_cpustate(cpu);
> +
> +    /*
> +     * Ensure we call kvm_arch_put_registers(). The vCPU isn't marked dirty if
> +     * it was parked in KVM and is now booting from a PSCI CPU_ON call.
> +     */
> +    cs->vcpu_dirty = true;
>  }
>  
>  void kvm_arm_create_host_vcpu(ARMCPU *cpu)

Also above my pay grade, but arm_set_cpu_on_async_work() which seems
to be what calls the CPU reset you refer to does a bunch of CPU register
and state setting including the power state setting that you mention.
Would the vcpu_dirty be better to go there?

Thanks,
Nick