Re: [PATCH] hw/intc/arm_gicv3_cpuif: Tolerate spurious EOIR writes

[Peter Maydell]

On Thu, 3 Jun 2021 at 12:01, Jean-Philippe Brucker
<jean-philippe@linaro.org> wrote:
>
> Commit 382c7160d1cd ("hw/intc/arm_gicv3_cpuif: Fix EOIR write access
> check logic") added an assert_not_reached() if the guest writes the EOIR
> register while no interrupt is active.
>
> It turns out some software does this: EDK2, in GicV3ExitBootServicesEvent(),
> unconditionally write EOIR for all interrupts that it manages. This now
> causes QEMU to abort when running UEFI on a VM with GICv3. Although it
> is UNPREDICTABLE behavior and EDK2 does need fixing, the punishment
> seems a little harsh, especially since icc_eoir_write() already
> tolerates writes of nonexistent interrupt numbers. Simply ignore
> spurious EOIR writes.
>
> Fixes: 382c7160d1cd ("hw/intc/arm_gicv3_cpuif: Fix EOIR write access check 
> logic")
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> ---
>  hw/intc/arm_gicv3_cpuif.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/hw/intc/arm_gicv3_cpuif.c b/hw/intc/arm_gicv3_cpuif.c
> index 81f94c7f4a..1d0964c9bf 100644
> --- a/hw/intc/arm_gicv3_cpuif.c
> +++ b/hw/intc/arm_gicv3_cpuif.c
> @@ -1357,7 +1357,8 @@ static void icc_eoir_write(CPUARMState *env, const 
> ARMCPRegInfo *ri,
>          }
>          break;
>      default:
> -        g_assert_not_reached();
> +        /* No interrupt was active, this is UNPREDICTABLE. Ignore it. */
> +        return;
>

Makes sense (and looking at the comment in icc_highest_active_group()
that says "return -1 so the caller ignores the spurious EOI attempt"
it is what the code originally intended).

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

Shashi, I guess this also fixes the assert you were seeing here ?

thanks
-- PMM