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xen: pvblock: fix the maximum io size in one operation

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The current implementation may cause BUG_ON() in blkfront_aio()
	BUG_ON(n > BLKIF_MAX_SEGMENTS_PER_REQUEST);

In pvblock_iop(), a read/write operation will be split into smaller
chunks of data so that the size in one access (aio_nbytes) is limited
to, at the maximum,
	BLKIF_MAX_SEGMENTS_PER_REQUEST * PAGE_SIZE

But this works only if when the *buffer* passed in to pvblock_io()
is page-aligned. If not, the given data region may stand across
(BLKIF_MAX_SEGMENTS_PER_REQUEST + 1) pages. See the logic in
blkfront_aio():
	start = (uintptr_t)aiocbp->aio_buf & PAGE_MASK;
	end = ((uintptr_t)aiocbp->aio_buf + aiocbp->aio_nbytes +
	       PAGE_SIZE - 1) & PAGE_MASK;
Then this will lead to BUG_ON() above.

This can be fixed by decreasing the maximum size of aio_nbytes.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Fixes: commit 3a739cc6c9 ("xen: pvblock: Implement front-back protocol and do IO")
This commit is contained in:
AKASHI Takahiro 2023-11-15 10:53:45 +09:00 committed by Tom Rini
parent d6d8078cb3
commit 654580eee1
1 changed files with 2 additions and 1 deletions
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3
drivers/xen/pvblock.c
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@ -632,7 +632,8 @@ static ulong pvblock_iop(struct udevice *udev, lbaint_t blknr,
memcpy(blk_dev->bounce_buffer, buffer, desc->blksz);
aiocb.aio_nbytes = unaligned ? desc->blksz :
min((size_t)(BLKIF_MAX_SEGMENTS_PER_REQUEST * PAGE_SIZE),
min((size_t)((BLKIF_MAX_SEGMENTS_PER_REQUEST - 1)
* PAGE_SIZE),
(size_t)(blocks_todo * desc->blksz));
blkfront_io(&aiocb, write);