Re: [PATCH Part2 v6 47/49] *fix for stale per-cpu pointer due to cond_resched during ghcb mapping

[Peter Gonda]

On Mon, Jun 20, 2022 at 5:15 PM Ashish Kalra <Ashish.Kalra@xxxxxxx> wrote:
>
> From: Michael Roth <michael.roth@xxxxxxx>
>
> Signed-off-by: Michael Roth <michael.roth@xxxxxxx>

Can you add a commit description here? Is this a fix for existing
SEV-ES support or should this be incorporated into a patch in this
series which adds this issue?

> ---
>  arch/x86/kvm/svm/svm.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index fced6ea423ad..f78e3b1bde0e 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -1352,7 +1352,7 @@ static void svm_vcpu_free(struct kvm_vcpu *vcpu)
>  static void svm_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
>  {
>         struct vcpu_svm *svm = to_svm(vcpu);
> -       struct svm_cpu_data *sd = per_cpu(svm_data, vcpu->cpu);
> +       struct svm_cpu_data *sd;
>
>         if (sev_es_guest(vcpu->kvm))
>                 sev_es_unmap_ghcb(svm);
> @@ -1360,6 +1360,10 @@ static void svm_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
>         if (svm->guest_state_loaded)
>                 return;
>
> +       /* sev_es_unmap_ghcb() can resched, so grab per-cpu pointer afterward. */
> +       barrier();
> +       sd = per_cpu(svm_data, vcpu->cpu);
> +
>         /*
>          * Save additional host state that will be restored on VMEXIT (sev-es)
>          * or subsequent vmload of host save area.
> --
> 2.25.1
>