[PATCH v3 1/2] nvmet-passthru: Limit mdts by BIO_MAX_PAGES

[PATCH v3 1/2] nvmet-passthru: Limit mdts by BIO_MAX_PAGES

[Logan Gunthorpe]

nvmet_passthru_map_sg() only supports mapping a single BIO, not a chain
so the effective maximum transfer should also be limitted by BIO_MAX_PAGES
(presently this works out to 1MB).

For PCI passthru devices the max_sectors would typically be more limitting
than BIO_MAX_PAGES, but this may not be true for all passthru devices.

Fixes: c1fef73f793b ("nvmet: add passthru code to process commands")
Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Sagi Grimberg <sagi@grimberg.me>
Cc: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Cc: Max Gurtovoy <mgurtovoy@nvidia.com>
---

v3: Added PG_TO_SECTOR constant which uses SECTOR_SHIFT (per Max)

 drivers/nvme/target/passthru.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/target/passthru.c b/drivers/nvme/target/passthru.c
index dacfa7435d0b..ed6b0586173e 100644
--- a/drivers/nvme/target/passthru.c
+++ b/drivers/nvme/target/passthru.c
@@ -22,11 +22,12 @@ static DEFINE_XARRAY(passthru_subsystems);

 static u16 nvmet_passthru_override_id_ctrl(struct nvmet_req *req)
 {
+	const int PG_TO_SECTOR = PAGE_SHIFT - SECTOR_SHIFT;
 	struct nvmet_ctrl *ctrl = req->sq->ctrl;
 	struct nvme_ctrl *pctrl = ctrl->subsys->passthru_ctrl;
 	u16 status = NVME_SC_SUCCESS;
 	struct nvme_id_ctrl *id;
-	u32 max_hw_sectors;
+	int max_hw_sectors;
 	int page_shift;

 	id = kzalloc(sizeof(*id), GFP_KERNEL);
@@ -45,9 +46,16 @@ static u16 nvmet_passthru_override_id_ctrl(struct nvmet_req *req)
 	 * which depends on the host's memory fragementation. To solve this,
 	 * ensure mdts is limited to the pages equal to the number of segments.
 	 */
-	max_hw_sectors = min_not_zero(pctrl->max_segments << (PAGE_SHIFT - 9),
+	max_hw_sectors = min_not_zero(pctrl->max_segments << PG_TO_SECTOR,
 				      pctrl->max_hw_sectors);

+	/*
+	 * nvmet_passthru_map_sg is limitted to using a single bio so limit
+	 * the mdts based on BIO_MAX_PAGES as well
+	 */
+	max_hw_sectors = min_not_zero(BIO_MAX_PAGES << PG_TO_SECTOR,
+				      max_hw_sectors);
+
 	page_shift = NVME_CAP_MPSMIN(ctrl->cap) + 12;

 	id->mdts = ilog2(max_hw_sectors) + 9 - page_shift;

base-commit: bbf5c979011a099af5dc76498918ed7df445635b
--
2.20.1

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[PATCH v3 2/2] nvmet-passthru: Cleanup nvmet_passthru_map_sg()

[Logan Gunthorpe]

Clean up some confusing elements of nvmet_passthru_map_sg() by returning
early if the request is greater than the maximum bio size. This allows
us to drop the sg_cnt variable.

This should not result in any functional change but makes the code
clearer and more understandable. The original code allocated a truncated
bio then would return EINVAL when bio_add_pc_page() filled that bio. The
new code just returns EINVAL early if this would happen.

Fixes: c1fef73f793b ("nvmet: add passthru code to process commands")
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Suggested-by: Douglas Gilbert <dgilbert@interlog.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
---
 drivers/nvme/target/passthru.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/target/passthru.c b/drivers/nvme/target/passthru.c
index ed6b0586173e..0e891a286fd8 100644
--- a/drivers/nvme/target/passthru.c
+++ b/drivers/nvme/target/passthru.c
@@ -188,18 +188,20 @@ static void nvmet_passthru_req_done(struct request *rq,
 
 static int nvmet_passthru_map_sg(struct nvmet_req *req, struct request *rq)
 {
-	int sg_cnt = req->sg_cnt;
 	struct scatterlist *sg;
 	int op_flags = 0;
 	struct bio *bio;
 	int i, ret;
 
+	if (req->sg_cnt > BIO_MAX_PAGES)
+		return -EINVAL;
+
 	if (req->cmd->common.opcode == nvme_cmd_flush)
 		op_flags = REQ_FUA;
 	else if (nvme_is_write(req->cmd))
 		op_flags = REQ_SYNC | REQ_IDLE;
 
-	bio = bio_alloc(GFP_KERNEL, min(sg_cnt, BIO_MAX_PAGES));
+	bio = bio_alloc(GFP_KERNEL, req->sg_cnt);
 	bio->bi_end_io = bio_put;
 	bio->bi_opf = req_op(rq) | op_flags;
 
@@ -209,7 +211,6 @@ static int nvmet_passthru_map_sg(struct nvmet_req *req, struct request *rq)
 			bio_put(bio);
 			return -EINVAL;
 		}
-		sg_cnt--;
 	}
 
 	ret = blk_rq_append_bio(rq, &bio);
-- 
2.20.1


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Re: [PATCH v3 1/2] nvmet-passthru: Limit mdts by BIO_MAX_PAGES

[Sagi Grimberg]

> diff --git a/drivers/nvme/target/passthru.c b/drivers/nvme/target/passthru.c
> index dacfa7435d0b..ed6b0586173e 100644
> --- a/drivers/nvme/target/passthru.c
> +++ b/drivers/nvme/target/passthru.c
> @@ -22,11 +22,12 @@ static DEFINE_XARRAY(passthru_subsystems);
> 
>   static u16 nvmet_passthru_override_id_ctrl(struct nvmet_req *req)
>   {
> +	const int PG_TO_SECTOR = PAGE_SHIFT - SECTOR_SHIFT;
>   	struct nvmet_ctrl *ctrl = req->sq->ctrl;
>   	struct nvme_ctrl *pctrl = ctrl->subsys->passthru_ctrl;
>   	u16 status = NVME_SC_SUCCESS;
>   	struct nvme_id_ctrl *id;
> -	u32 max_hw_sectors;
> +	int max_hw_sectors;
>   	int page_shift;
> 
>   	id = kzalloc(sizeof(*id), GFP_KERNEL);
> @@ -45,9 +46,16 @@ static u16 nvmet_passthru_override_id_ctrl(struct nvmet_req *req)
>   	 * which depends on the host's memory fragementation. To solve this,
>   	 * ensure mdts is limited to the pages equal to the number of segments.
>   	 */
> -	max_hw_sectors = min_not_zero(pctrl->max_segments << (PAGE_SHIFT - 9),
> +	max_hw_sectors = min_not_zero(pctrl->max_segments << PG_TO_SECTOR,
>   				      pctrl->max_hw_sectors);

I also liked the previous one better...

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