Re: [PATCH v2 1/2] tests/avocado: use default amount of cores on sbsa-ref

[Peter Maydell]

On Thu, 20 Jun 2024 at 10:55, Marcin Juszkiewicz
<marcin.juszkiewicz@linaro.org> wrote:
>
> W dniu 20.06.2024 o 11:34, Peter Maydell pisze:
> > On Thu, 20 Jun 2024 at 07:00, Marcin Juszkiewicz
> > <marcin.juszkiewicz@linaro.org> wrote:
> >>
> >> I was wondering why avocado tests passed with firmware which
> >> crashes when anyone else is using it.
> >>
> >> Turned out that amount of cores matters. Have to find out why
> >> still.
> >
> > This commit message confuses me.
>
> Had no idea how to write in more readable form. Will reword it for v3
> (with reverse order of patches as recommended by Philippe.
>
> > It reads like "running with two cores will make the guest crash",
> > i.e. "apply this patch and the test suite will stop passing". I
> > assume that's not the case, but what's actually going on here?
>
> That's exactly the case. With sbsa-ref firmware which qemu uses now we
> have crash if more than 1 core is used. Avocado test hardcoded "-smp 1"
> and was passing fine.
>
> And I forgot to mail qemu-devel when I got hit by that crash.
>
> This week Rebecca Cran pointed me that crash is in BootLogoLib in EDK2
> and I wrote some workaround for make things work. Then Ard Biesheuvel
> found the real reason, fixed QemuVideoDxe in EDK2 and we got sbsa-ref
> running with any amount of cores.

Oh, OK, so it's just random bad luck that enabling the second
CPU means that we end up doing an unaligned access to the
framebuffer, I guess.

Then, yes, Philippe is right and we need to update our sbsa-ref
firmware we're using for the test first, to avoid breaking bisection.

For a commit message for this patch, maybe something like:

 The version of the sbsa-ref EDK2 firmware we used to use in this
 test had a bug where it might make an unaligned access to the
 framebuffer, which causes a guest crash on newer versions of
 QEMU where we enforce the architectural requirement that
 unaligned accesses to Device memory should take an exception.
 We happened to not notice this because our test was booting with
 "-smp 1" and through luck this didn't write the boot logo to
 the framebuffer at an unaligned address; but trying to boot the
 same firmware with two CPUs would result in a guest crash.
 Now we have updated the firmware we're using for the test, we can
 make the test use all the cores on the board, so we are testing the
 SMP boot path.

?

thanks
-- PMM