On Mon, Feb 8, 2021 at 11:10 PM David Gow <davidgow@xxxxxxxxxx> 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@xxxxxxxxxx>
Reviewed-by: Brendan Higgins <brendanhiggins@xxxxxxxxxx>
