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Date:   Fri, 26 Feb 2021 12:57:32 -0800
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     David Gow <davidgow@...gle.com>
Cc:     Shuah Khan <skhan@...uxfoundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        KUnit Development <kunit-dev@...glegroups.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        linux-um <linux-um@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kunit: tool: Disable PAGE_POISONING under --alltests

On Mon, Feb 8, 2021 at 11:10 PM David Gow <davidgow@...gle.com> wrote:
>
> kunit_tool maintains a list of config options which are broken under
> UML, which we exclude from an otherwise 'make ARCH=um allyesconfig'
> build used to run all tests with the --alltests option.
>
> Something in UML allyesconfig is causing segfaults when page poisining
> is enabled (and is poisoning with a non-zero value). Previously, this
> didn't occur, as allyesconfig enabled the CONFIG_PAGE_POISONING_ZERO
> option, which worked around the problem by zeroing memory. This option
> has since been removed, and memory is now poisoned with 0xAA, which
> triggers segfaults in many different codepaths, preventing UML from
> booting.
>
> Note that we have to disable both CONFIG_PAGE_POISONING and
> CONFIG_DEBUG_PAGEALLOC, as the latter will 'select' the former on
> architectures (such as UML) which don't implement __kernel_map_pages().
>
> Ideally, we'd fix this properly by tracking down the real root cause,
> but since this is breaking KUnit's --alltests feature, it's worth
> disabling there in the meantime so the kernel can boot to the point
> where tests can actually run.
>
> Fixes: f289041ed4 ("mm, page_poison: remove CONFIG_PAGE_POISONING_ZERO")
> Signed-off-by: David Gow <davidgow@...gle.com>

Reviewed-by: Brendan Higgins <brendanhiggins@...gle.com>

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