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References: <20231115203401.2495875-1-iii@linux.ibm.com> <20231115203401.2495875-8-iii@linux.ibm.com>
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From:   Alexander Potapenko <glider@google.com>
Date:   Thu, 16 Nov 2023 11:52:10 +0100
Message-ID: <CAG_fn=WcuQxB6ZRKwi221EM-QsEfJ7udyQg9W_z0jv9nFCB89A@mail.gmail.com>
Subject: Re: [PATCH 07/32] kmsan: Remove a useless assignment from kmsan_vmap_pages_range_noflush()
To:     Ilya Leoshkevich <iii@linux.ibm.com>
Cc:     Alexander Gordeev <agordeev@linux.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Marco Elver <elver@google.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Pekka Enberg <penberg@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>,
        kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-s390@vger.kernel.org,
        linux-trace-kernel@vger.kernel.org,
        Mark Rutland <mark.rutland@arm.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Sven Schnelle <svens@linux.ibm.com>
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On Wed, Nov 15, 2023 at 9:34=E2=80=AFPM Ilya Leoshkevich <iii@linux.ibm.com=
> wrote:
>
> The value assigned to prot is immediately overwritten on the next line
> with PAGE_KERNEL. The right hand side of the assignment has no
> side-effects.
>
> Fixes: b073d7f8aee4 ("mm: kmsan: maintain KMSAN metadata for page operati=
ons")
> Suggested-by: Alexander Gordeev <agordeev@linux.ibm.com>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Alexander Potapenko <glider@google.com>

> ---
>  mm/kmsan/shadow.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/mm/kmsan/shadow.c b/mm/kmsan/shadow.c
> index b9d05aff313e..2d57408c78ae 100644
> --- a/mm/kmsan/shadow.c
> +++ b/mm/kmsan/shadow.c
> @@ -243,7 +243,6 @@ int kmsan_vmap_pages_range_noflush(unsigned long star=
t, unsigned long end,
>                 s_pages[i] =3D shadow_page_for(pages[i]);
>                 o_pages[i] =3D origin_page_for(pages[i]);
>         }
> -       prot =3D __pgprot(pgprot_val(prot) | _PAGE_NX);
>         prot =3D PAGE_KERNEL;

This bug dates back to 5.1-rc2, when KMSAN didn't exist upstream.
The commit introducing vmap support already had it:
https://github.com/google/kmsan/commit/3ff9d7c640d378485286e1a99d85984ae690=
1f23
I don't remember what exactly required the more relaxed PAGE_KERNEL
mask though :)