Re: [PATCH] dma-helpers: Fix iovec alignment

[Philippe Mathieu-Daudé]

On 12/4/24 10:06, Stefan Fritsch wrote:
> Commit 99868af3d0 changed the hardcoded constant BDRV_SECTOR_SIZE to a
> dynamic field 'align' but introduced a bug. qemu_iovec_discard_back()
> is now passed the wanted iov length instead of the actually required
> amount that should be removed from the end of the iov.
>
> The bug can likely only be hit in uncommon configurations, e.g. with
> icount enabled or when reading from disk directly to device memory.
>
> Fixes: 99868af3d0a75cf6 ("dma-helpers: explicitly pass alignment into DMA 
> helpers")

Cc'ing developers mentioned in this commit.

> Signed-off-by: Stefan Fritsch <sf@sfritsch.de>
> ---
>   system/dma-helpers.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/system/dma-helpers.c b/system/dma-helpers.c
> index 9b221cf94e..c9677fd39b 100644
> --- a/system/dma-helpers.c
> +++ b/system/dma-helpers.c
> @@ -174,8 +174,7 @@ static void dma_blk_cb(void *opaque, int ret)
>       }
>   
>       if (!QEMU_IS_ALIGNED(dbs->iov.size, dbs->align)) {
> -        qemu_iovec_discard_back(&dbs->iov,
> -                                QEMU_ALIGN_DOWN(dbs->iov.size, dbs->align));
> +        qemu_iovec_discard_back(&dbs->iov, dbs->iov.size % dbs->align);
>       }
>   
>       dbs->acb = dbs->io_func(dbs->offset, &dbs->iov,