From: Ira Weiny <[email protected]>
To: "Fabio M. De Francesco" <[email protected]>
Cc: Benjamin LaHaise <[email protected]>,
Alexander Viro <[email protected]>,
Eric Biederman <[email protected]>,
Kees Cook <[email protected]>,
Dan Williams <[email protected]>,
"Matthew Wilcox" <[email protected]>, Jan Kara <[email protected]>,
Jeff Layton <[email protected]>,
Chuck Lever <[email protected]>,
Jens Axboe <[email protected]>,
Pavel Begunkov <[email protected]>,
Thomas Gleixner <[email protected]>,
Paul Walmsley <[email protected]>,
"Palmer Dabbelt" <[email protected]>,
Albert Ou <[email protected]>,
"Nathan Chancellor" <[email protected]>,
Nick Desaulniers <[email protected]>,
Tom Rix <[email protected]>, <[email protected]>,
<[email protected]>, <[email protected]>,
<[email protected]>, <[email protected]>,
<[email protected]>, <[email protected]>,
<[email protected]>
Subject: Re: [PATCH] fs: Call kmap_local_page() in copy_string_kernel()
Date: Thu, 21 Jul 2022 17:14:20 -0700 [thread overview]
Message-ID: <Ytnr3IhSkDOjqbZ1@iweiny-desk3> (raw)
In-Reply-To: <[email protected]>
On Sun, Jul 10, 2022 at 12:01:36PM +0200, Fabio M. De Francesco wrote:
> The use of kmap_atomic() is being deprecated in favor of kmap_local_page().
>
> With kmap_local_page(), the mappings are per thread, CPU local, not
> globally visible and can take page faults. Furthermore, the mappings can be
> acquired from any context (including interrupts).
>
> Therefore, use kmap_local_page() in copy_string_kernel() instead of
> kmap_atomic().
>
> Tested with xfstests on a QEMU + KVM 32-bits VM booting a kernel with
> HIGHMEM64GB enabled.
>
> Suggested-by: Ira Weiny <[email protected]>
> Signed-off-by: Fabio M. De Francesco <[email protected]>
> ---
>
> I sent a first patch to fs/exec.c for converting kmap() and kmap_atomic()
> to kmap_local_page():
> https://lore.kernel.org/lkml/[email protected]/
>
> Some days ago, Ira Weiny, while he was reviewing that patch, made me notice
> that I had overlooked a second kmap_atomic() in the same file (thanks):
> https://lore.kernel.org/lkml/YsiQptk19txHrG4c@iweiny-desk3/
>
> I've been asked to send this as an additional change. This is why there will
> not be any second version of that previous patch.
>
> fs/exec.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index 4a2129c0d422..5fa652ca5823 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -639,11 +639,11 @@ int copy_string_kernel(const char *arg, struct linux_binprm *bprm)
> page = get_arg_page(bprm, pos, 1);
> if (!page)
> return -E2BIG;
> - kaddr = kmap_atomic(page);
> + kaddr = kmap_local_page(page);
> flush_arg_page(bprm, pos & PAGE_MASK, page);
I really question why we can't use memcpy_to_page() here and move the
flush_arg_page() prior to the mapping?
flush_arg_page() only calls flush_cache_page() which does not need the
mapping to work correctly AFAICT.
Ira
> memcpy(kaddr + offset_in_page(pos), arg, bytes_to_copy);
> flush_dcache_page(page);
> - kunmap_atomic(kaddr);
> + kunmap_local(kaddr);
> put_arg_page(page);
> }
>
> --
> 2.36.1
>
next prev parent reply other threads:[~2022-07-22 0:14 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-10 10:01 [PATCH] fs: Call kmap_local_page() in copy_string_kernel() Fabio M. De Francesco
2022-07-22 0:14 ` Ira Weiny [this message]
2022-07-23 1:02 ` Fabio M. De Francesco
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