Re: [PATCH] scsi: megaraid_sas: fix PRP list out-of-bounds write

Thorsten,

> Martin, do you know if someone there ever looked into this regression
> and the proposed fix? I'm wondering because Daniel and Mats reported
> problems under the same subject line (in new threads), but also didn't
> get a reply.

I think this problem is just an unfortunate side effect of the kernel
being able to build bigger I/Os by default.

Typically NVMe SSDs report fairly modest maximum I/O sizes compared to
SCSI devices. I suspect this is why we only see this issue with a few
select models. My hunch is that these drives advertise a fairly large
MDTS.

Since there appears to be no traction wrt. fixing the MR PRP vs. SGL
chaining logic, I wonder if the patch below is sufficient?

-- 
Martin K. Petersen

diff --git a/drivers/scsi/megaraid/megaraid_sas_base.c b/drivers/scsi/megaraid/megaraid_sas_base.c
index ecd365d78ae3..b93a6d1180ff 100644
--- a/drivers/scsi/megaraid/megaraid_sas_base.c
+++ b/drivers/scsi/megaraid/megaraid_sas_base.c
@@ -1978,7 +1978,8 @@ megasas_set_nvme_device_properties(struct scsi_device *sdev,
 	mr_nvme_pg_size = max_t(u32, instance->nvme_page_size,
 				MR_DEFAULT_NVME_PAGE_SIZE);
 
-	lim->max_hw_sectors = max_io_size / 512;
+	lim->max_hw_sectors =
+		min(SZ_2M >> SECTOR_SHIFT, max_io_size >> SECTOR_SHIFT);
 	lim->virt_boundary_mask = mr_nvme_pg_size - 1;
 }