[PATCH v2 1/2] nvmet-passthru: Limit mdts by BIO_MAX_PAGES

[Max Gurtovoy]

On 10/17/2020 1:19 AM, Logan Gunthorpe wrote:
> 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 at lst.de>
> Signed-off-by: Logan Gunthorpe <logang at deltatee.com>
> Cc: Christoph Hellwig <hch at lst.de>
> Cc: Sagi Grimberg <sagi at grimberg.me>
> Cc: Chaitanya Kulkarni <chaitanya.kulkarni at wdc.com>
> ---
>   drivers/nvme/target/passthru.c | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/nvme/target/passthru.c b/drivers/nvme/target/passthru.c
> index dacfa7435d0b..1ab88df3310f 100644
> --- a/drivers/nvme/target/passthru.c
> +++ b/drivers/nvme/target/passthru.c
> @@ -26,7 +26,7 @@ static u16 nvmet_passthru_override_id_ctrl(struct nvmet_req *req)
>   	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);
> @@ -48,6 +48,13 @@ static u16 nvmet_passthru_override_id_ctrl(struct nvmet_req *req)
>   	max_hw_sectors = min_not_zero(pctrl->max_segments << (PAGE_SHIFT - 9),
>   				      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 << (PAGE_SHIFT - 9),
> +				      max_hw_sectors);

can 9 be replaced with SECTOR_SHIFT ?


> +
>   	page_shift = NVME_CAP_MPSMIN(ctrl->cap) + 12;
>   
>   	id->mdts = ilog2(max_hw_sectors) + 9 - page_shift;
>
> base-commit: bbf5c979011a099af5dc76498918ed7df445635b