Re: [PATCH v3] mpt3sas: Limit NVMe request size to 2 MiB

[David Laight <david.laight.linux@gmail.com>]

On Mon, 13 Apr 2026 23:30:03 +0530
Ranjan Kumar <ranjan.kumar@broadcom.com> wrote:

> The HBA firmware reports NVMe MDTS values based on the underlying drive
> capability. However, due to the 4K PRP page size and a limit of
> 512 entries, the driver supports a maximum I/O transfer size of 2 MiB.
> 
> Limit max_hw_sectors to the smaller of the reported MDTS and the
> 2 MiB driver limit to prevent issuing oversized I/O that may lead
> to a kernel oops.
> 
> Cc: stable@vger.kernel.org
> Fixes: 9b8b84879d4a ("block: Increase BLK_DEF_MAX_SECTORS_CAP")
> Reported-by: Mira Limbeck <m.limbeck@proxmox.com>
> Closes: https://lore.kernel.org/r/291f78bf-4b4a-40dd-867d-053b36c564b3@proxmox.com
> Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9b8b84879d4a
> Suggested-by: Keith Busch <kbusch@kernel.org>
> Signed-off-by: Ranjan Kumar <ranjan.kumar@broadcom.com>
> ---
>  drivers/scsi/mpt3sas/mpt3sas_scsih.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/mpt3sas/mpt3sas_scsih.c b/drivers/scsi/mpt3sas/mpt3sas_scsih.c
> index 6ff788557294..44dd439e6f17 100644
> --- a/drivers/scsi/mpt3sas/mpt3sas_scsih.c
> +++ b/drivers/scsi/mpt3sas/mpt3sas_scsih.c
> @@ -2738,8 +2738,20 @@ scsih_sdev_configure(struct scsi_device *sdev, struct queue_limits *lim)
>  				pcie_device->enclosure_level,
>  				pcie_device->connector_name);
>  
> +		/*
> +		 * The HBA firmware passes the NVMe drive's MDTS
> +		 * (Maximum Data Transfer Size) up to the driver. However,
> +		 * the driver hardcodes a 4K page size for the PRP list,
                                             ^ buffer ? 
> +		 * accommodating at most 512 entries. This strictly limits
> +		 * the maximum supported NVMe I/O transfer to 2 MiB.

Doesn't that make max_fw_entries 4096/8.
Assuming 4096 byte sectors the longest transfer is then 4096/8*4096.
So none of this has anything to to with SECTOR_SHIFT.

> +		 *
> +		 * Cap max_hw_sectors to the smaller of the drive's reported
> +		 * MDTS or the 2 MiB driver limit to prevent kernel oopses.
> +		 */
> +		lim->max_hw_sectors = SZ_2M >> SECTOR_SHIFT;
>  		if (pcie_device->nvme_mdts)
> -			lim->max_hw_sectors = pcie_device->nvme_mdts / 512;
> +			lim->max_hw_sectors = min_t(u32, lim->max_hw_sectors,
> +					pcie_device->nvme_mdts >> SECTOR_SHIFT);

Why min_t() ?

David

>  
>  		pcie_device_put(pcie_device);
>  		spin_unlock_irqrestore(&ioc->pcie_device_lock, flags);