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Date:   Thu, 21 Sep 2023 17:28:28 +0100
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Subject: Re: [PATCH v4 8/8] selftests/mm: add uffd unit test for UFFDIO_POISON
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To:     Axel Rasmussen <axelrasmussen@google.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Brian Geffon <bgeffon@google.com>,
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        Muchun Song <muchun.song@linux.dev>,
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        Suren Baghdasaryan <surenb@google.com>,
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References: <20230707215540.2324998-1-axelrasmussen@google.com>
 <20230707215540.2324998-9-axelrasmussen@google.com>
From:   Ryan Roberts <ryan.roberts@arm.com>
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On 07/07/2023 22:55, Axel Rasmussen wrote:
> The test is pretty basic, and exercises UFFDIO_POISON straightforwardly.
> We register a region with userfaultfd, in missing fault mode. For each
> fault, we either UFFDIO_COPY a zeroed page (odd pages) or UFFDIO_POISON
> (even pages). We do this mix to test "something like a real use case",
> where guest memory would be some mix of poisoned and non-poisoned pages.
> 
> We read each page in the region, and assert that the odd pages are
> zeroed as expected, and the even pages yield a SIGBUS as expected.
> 
> Why UFFDIO_COPY instead of UFFDIO_ZEROPAGE? Because hugetlb doesn't
> support UFFDIO_ZEROPAGE, and we don't want to have special case code.
> 
> Acked-by: Peter Xu <peterx@redhat.com>
> Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>

Hi,

FYI, when running this test on arm64 it provokes a kernel panic. I've posted a
fix along with a detailed explanation at [1].

[1]
https://lore.kernel.org/linux-arm-kernel/20230921162007.1630149-1-ryan.roberts@arm.com/

Thanks,
Ryan