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In-Reply-To: <f09d851d-bda1-7a99-41cb-a14ea51e1237@yandex.ru>
From:   Jim Mattson <jmattson@google.com>
Date:   Fri, 25 Jun 2021 17:15:29 -0700
Message-ID: <CALMp9eQWKa1vL+jj5HXO1bm+oMo6gQLNw44P7y6ZaF8_WQfukw@mail.gmail.com>
Subject: Re: exception vs SIGALRM race on core2 CPUs (with fix!)
To:     stsp <stsp2@yandex.ru>
Cc:     Sean Christopherson <seanjc@google.com>, kvm@vger.kernel.org
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On Fri, Jun 25, 2021 at 4:35 PM stsp <stsp2@yandex.ru> wrote:
>
> OK, I've finally found that this
> fixes the race:
>
> --- x86.c.old   2021-03-20 12:51:14.000000000 +0300
> +++ x86.c       2021-06-26 02:28:37.082919492 +0300
> @@ -9176,8 +9176,10 @@
>                  if (__xfer_to_guest_mode_work_pending()) {
>                          srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
>                          r = xfer_to_guest_mode_handle_work(vcpu);
> -                       if (r)
> +                       if (r) {
> +kvm_clear_exception_queue(vcpu);
>                                  return r;
> +}
>                          vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
>                  }
>          }
>
>
>
> This is where it returns to user
> with the PF exception still pending.
> So... any ideas?

If the squashed exception was a trap, it's now lost.