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virtio: console: Replace deprecated kmap_atomic with kmap_local_page

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kmap_atomic() is deprecated and should be replaced with kmap_local_page()
[1][2]. kmap_local_page() is faster in kernels with HIGHMEM enabled, can
take page faults, and allows preemption.

According to [2], this replacement is safe as long as the code between
kmap_atomic() and kunmap_atomic() does not implicitly depend on disabling
page faults or preemption. In this patch, the only thing happening between
mapping and unmapping the page is a memcpy, and I don't suspect it depends
on disabling page faults or preemption.

[1] https://lwn.net/Articles/836144/
[2] https://docs.kernel.org/mm/highmem.html#temporary-virtual-mappings

Signed-off-by: David Reaver <me@davidreaver.com>
Reviewed-by: Amit Shah <amit@kernel.org>
Link: https://lore.kernel.org/r/20250109035904.168345-1-me@davidreaver.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
David Reaver 2025-01-08 19:59:02 -08:00 committed by Greg Kroah-Hartman
parent a01f6287c2
commit 4cabaa0517
1 changed files with 2 additions and 2 deletions
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4
drivers/char/virtio_console.c
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@ -883,9 +883,9 @@ static int pipe_to_sg(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
if (len + offset > PAGE_SIZE)
len = PAGE_SIZE - offset;
src = kmap_atomic(buf->page);
src = kmap_local_page(buf->page);
memcpy(page_address(page) + offset, src + buf->offset, len);
kunmap_atomic(src);
kunmap_local(src);
sg_set_page(&(sgl->sg[sgl->n]), page, len, offset);
}