linux-kernel - Re: [PATCH v2 5/6] selftests/mm: add uffd unit test for UFFDIO

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Message-ID: <ZKSMBnLkGXhlcwWs@x1n>
Date:   Tue, 4 Jul 2023 17:15:50 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Axel Rasmussen <axelrasmussen@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Brauner <brauner@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Huang Ying <ying.huang@...el.com>,
        Hugh Dickins <hughd@...gle.com>,
        James Houghton <jthoughton@...gle.com>,
        Jiaqi Yan <jiaqiyan@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "Mike Rapoport (IBM)" <rppt@...nel.org>,
        Muchun Song <muchun.song@...ux.dev>,
        Nadav Amit <namit@...are.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Shuah Khan <shuah@...nel.org>,
        ZhangPeng <zhangpeng362@...wei.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 5/6] selftests/mm: add uffd unit test for UFFDIO_POISON

On Thu, Jun 29, 2023 at 01:50:39PM -0700, 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.
> 
> Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>

Acked-by: Peter Xu <peterx@...hat.com>

-- 
Peter Xu