Re: mainline/master bisection: baseline.login on meson-sm1-khadas-vim3l
From: Marc Zyngier
Date: Wed Feb 24 2021 - 03:53:54 EST
On 2021年2月23日 21:03:52 +0000,
Guillaume Tucker <guillaume.tucker@xxxxxxxxxxxxx> wrote:
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On 23/02/2021 14:18, Marc Zyngier wrote:
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> Hi Guillaume,
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> On 2021年2月23日 09:46:30 +0000,
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> Guillaume Tucker <guillaume.tucker@xxxxxxxxxxxxx> wrote:
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>>
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>> Hello Marc,
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>>
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>> Please see the bisection report below about a boot failure on
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>> meson-sm1-khadas-vim3l on mainline. It seems to only be
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>> affecting kernels built with CONFIG_ARM64_64K_PAGES=y.
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>>
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>> Reports aren't automatically sent to the public while we're
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>> trialing new bisection features on kernelci.org but this one
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>> looks valid.
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>>
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>> There's no output in the log, so the kernel is most likely
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>> crashing early. Some more details can be found here:
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>>
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>> https://kernelci.org/test/case/id/6034bed3b344e2860daddcc8/
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>>
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>> Please let us know if you need any help to debug the issue or try
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>> a fix on this platform.
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> Thanks for the heads up.
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> There is actually a fundamental problem with the patch you bisected
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> to: it provides no guarantee that the point where we enable the EL2
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> MMU is in the idmap and, as it turns out, the code we're running from
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> disappears from under our feet, leading to a translation fault we're
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> not prepared to handle.
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> How does it work with 4kB pages? Luck.
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There may be a fascinating explanation for it, but luck works
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too. It really seems to be booting happily with 4k pages:
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https://kernelci.org/test/plan/id/60347b358de339d1b7addcc5/
Oh, I know it boots fine with 4k, that's what I used everywhere.
We're just lucky that the bit of code that deals with the MMU happens
to *also* be in the idmap. With 64k pages, it gets pushed further down
the line, and bad things happen. Short of explicit statements in the
code, luck rules.
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> Do you mind giving the patch below a go? It does work on my vim3l and
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> on a FVP, so odds are that it will solve it for you too.
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Sure, and that worked here as well:
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http://lava.baylibre.com:10080/scheduler/job/752416
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and here's the test branch where I applied your fix, for
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completeness:
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https://gitlab.collabora.com/gtucker/linux/-/commits/v5.11-vim3l-vhe/
Awesome. thanks for having tested it.
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As always, if you do send a patch with the fix, please give some
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credit to the bot:
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Reported-by: "kernelci.org bot" <bot@xxxxxxxxxxxx>
Will do. Mind if I credit you too for the testing?
Thanks,
M.
--
Without deviation from the norm, progress is not possible.