On 10/20/26 5:55 AM, Shubham Antil wrote:
The misaligned I/O fallback copies the full bounce scatterlist to the request buffer during completion. If a data-in command transfers less than requested, part of a newly allocated bounce page can remain unwritten.Allocate bounce pages with __GFP_ZERO so all bytes copied during completion have a defined value. This path is already the slow fallback for misaligned I/O, so the added initialization cost is acceptable. Found during an LLM-assisted source audit and validated with a QEMU/KVM vhost-scsi target using misaligned data-in commands. Fixes: 5ced58bfa132 ("vhost-scsi: Fix alignment handling with windows") Cc: [email protected] Assisted-by: LLM (OpenAI Codex, gpt-5.6-sol) Signed-off-by: Shubham Antil <[email protected]> --- Changes in v3: - Restore allocation-time zeroing after review confirmed that this is an already slow and uncommon bounce-buffer fallback. - Keep the change minimal and document why the zeroing is required. - Drop the transfer-length copy-back change from v2. - Add the discovery method and the requested Fixes, stable Cc, Assisted-by, and Signed-off-by tags. drivers/vhost/scsi.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c index 885fac5ed042..8493a372de6c 100644 --- a/drivers/vhost/scsi.c +++ b/drivers/vhost/scsi.c @@ -937,7 +937,12 @@ vhost_scsi_copy_iov_to_sgl(struct vhost_scsi_cmd *cmd, struct iov_iter *iter, }for_each_sgtable_sg(sg_table, sg, i) {- page = alloc_page(GFP_KERNEL); + /* + * Completion copies the full bounce buffer, including bytes the + * target did not write. This is already the slow fallback for + * misaligned I/O, so zeroing is acceptable here. + */ + page = alloc_page(GFP_KERNEL | __GFP_ZERO); if (!page) { ret = -ENOMEM; goto err;
Reviewed-by: Mike Christie <[email protected]>
