Re: [PATCH v2 1/2] target/arm: kvm: Inject events at the last stage of sync

From: Andrew Jones <drjones@redhat.com>
To: Beata Michalska <beata.michalska@linaro.org>
Cc: qemu-devel@nongnu.org, qemu-arm@nongnu.org, pbonzini@redhat.com,
	kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH v2 1/2] target/arm: kvm: Inject events at the last stage of sync
Date: Tue, 4 Feb 2020 11:34:47 +0100	[thread overview]
Message-ID: <20200204103447.naw26xl2y2zbyrqb@kamzik.brq.redhat.com> (raw)
In-Reply-To: <20200129202441.12745-2-beata.michalska@linaro.org>

On Wed, Jan 29, 2020 at 08:24:40PM +0000, Beata Michalska wrote:
> KVM_SET_VCPU_EVENTS might actually lead to vcpu registers being modified.
> As such this should be the last step of sync to avoid potential overwriting
> of whatever changes KVM might have done.
> 
> Signed-off-by: Beata Michalska <beata.michalska@linaro.org>
> ---
>  target/arm/kvm32.c | 20 ++++++++++----------
>  target/arm/kvm64.c | 20 ++++++++++----------
>  2 files changed, 20 insertions(+), 20 deletions(-)
> 
> diff --git a/target/arm/kvm32.c b/target/arm/kvm32.c
> index 32bf8d6..cf2b47f 100644
> --- a/target/arm/kvm32.c
> +++ b/target/arm/kvm32.c
> @@ -386,17 +386,17 @@ int kvm_arch_put_registers(CPUState *cs, int level)
>          return ret;
>      }
>  
> -    ret = kvm_put_vcpu_events(cpu);
> -    if (ret) {
> -        return ret;
> -    }
> -
>      write_cpustate_to_list(cpu, true);
>  
>      if (!write_list_to_kvmstate(cpu, level)) {
>          return EINVAL;
>      }
>  
> +    ret = kvm_put_vcpu_events(cpu);
> +    if (ret) {
> +        return ret;
> +    }
> +

I think we should put a comment above this that says basically the same
thing as the commit message in order to explain why kvm_put_vcpu_events()
*must* be after write_list_to_kvmstate().

>      kvm_arm_sync_mpstate_to_kvm(cpu);
>  
>      return ret;
> @@ -462,11 +462,6 @@ int kvm_arch_get_registers(CPUState *cs)
>      }
>      vfp_set_fpscr(env, fpscr);
>  
> -    ret = kvm_get_vcpu_events(cpu);
> -    if (ret) {
> -        return ret;
> -    }
> -
>      if (!write_kvmstate_to_list(cpu)) {
>          return EINVAL;
>      }
> @@ -475,6 +470,11 @@ int kvm_arch_get_registers(CPUState *cs)
>       */
>      write_list_to_cpustate(cpu);
>  
> +    ret = kvm_get_vcpu_events(cpu);
> +    if (ret) {
> +        return ret;
> +    }
> +

Why are we moving kvm_get_vcpu_events()?

>      kvm_arm_sync_mpstate_to_qemu(cpu);
>  
>      return 0;
> diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c
> index 6344113..d06fd32 100644
> --- a/target/arm/kvm64.c
> +++ b/target/arm/kvm64.c
> @@ -1043,17 +1043,17 @@ int kvm_arch_put_registers(CPUState *cs, int level)
>          return ret;
>      }
>  
> -    ret = kvm_put_vcpu_events(cpu);
> -    if (ret) {
> -        return ret;
> -    }
> -
>      write_cpustate_to_list(cpu, true);
>  
>      if (!write_list_to_kvmstate(cpu, level)) {
>          return -EINVAL;
>      }
>  
> +    ret = kvm_put_vcpu_events(cpu);
> +    if (ret) {
> +        return ret;
> +    }
> +
>      kvm_arm_sync_mpstate_to_kvm(cpu);
>  
>      return ret;
> @@ -1251,11 +1251,6 @@ int kvm_arch_get_registers(CPUState *cs)
>      }
>      vfp_set_fpcr(env, fpr);
>  
> -    ret = kvm_get_vcpu_events(cpu);
> -    if (ret) {
> -        return ret;
> -    }
> -
>      if (!write_kvmstate_to_list(cpu)) {
>          return -EINVAL;
>      }
> @@ -1264,6 +1259,11 @@ int kvm_arch_get_registers(CPUState *cs)
>       */
>      write_list_to_cpustate(cpu);
>  
> +    ret = kvm_get_vcpu_events(cpu);
> +    if (ret) {
> +        return ret;
> +    }
> +
>      kvm_arm_sync_mpstate_to_qemu(cpu);
>  
>      /* TODO: other registers */
> -- 
> 2.7.4
> 
> 

Same comments for kvm64.c as for kvm32.c

Thanks,
drew

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