From: Peter Xu <peterx@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-kselftest@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Shuah Khan <shuah@kernel.org>
Subject: Re: [PATCH v1] selftests: mm: gup_longterm: test unsharing logic when R/O pinning
Date: Tue, 30 Apr 2024 09:36:05 -0400 [thread overview]
Message-ID: <ZjDzxcrP_tDxo-X6@x1n> (raw)
In-Reply-To: <20240430131508.86924-1-david@redhat.com>
On Tue, Apr 30, 2024 at 03:15:08PM +0200, David Hildenbrand wrote:
> In our FOLL_LONGTERM tests, we prefault the page tables for the GUP-fast
> test cases to be able to find a PTE and exercise the "longterm pinning
> allowed" logic on the GUP-fast path where possible.
>
> For now, we always prefault the page tables writable, resulting in PTEs
> that are writable.
>
> Let's cover more cases to also test if our unsharing logic works as
> expected (and is able to make progress when there is nothing to unshare)
> by mprotect'ing the range R/O when R/O-pinning, so we don't get PTEs
> that are writable.
>
> This change would have found an issue introduced by commit a12083d721d7
> ("mm/gup: handle hugepd for follow_page()"), whereby R/O pinning was not
> able to make progress in all cases, because unsharing logic was not
> provided with the VMA to decide at some point that long-term R/O pinning
> a !anon page is fine.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Peter Xu <peterx@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Peter Xu <peterx@redhat.com>
Thanks,
--
Peter Xu
prev parent reply other threads:[~2024-04-30 13:36 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-30 13:15 [PATCH v1] selftests: mm: gup_longterm: test unsharing logic when R/O pinning David Hildenbrand
2024-04-30 13:36 ` Peter Xu [this message]
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