Phil Oester reported that a fix for a possible buffer overrun that I sent
caused a regression that manifests in this output:

 Event Message: A PCI parity error was detected on a component at bus 0 device 5 function 0.
 Severity: Critical
 Message ID: PCI1308

The original code tried to handle the sense data pointer differently when
using 32-bit 64-bit DMA addressing, which would lead to a 32-bit dma_addr_t
value of 0x11223344 to get stored

32-bit kernel:       44 33 22 11 ?? ?? ?? ??
64-bit LE kernel:    44 33 22 11 00 00 00 00
64-bit BE kernel:    00 00 00 00 44 33 22 11

or a 64-bit dma_addr_t value of 0x1122334455667788 to get stored as

32-bit kernel:       88 77 66 55 ?? ?? ?? ??
64-bit kernel:       88 77 66 55 44 33 22 11

In my patch, I tried to ensure that the same value is used on both 32-bit
and 64-bit kernels, and picked what seemed to be the most sensible
combination, storing 32-bit addresses in the first four bytes (as 32-bit
kernels already did), and 64-bit addresses in eight consecutive bytes (as
64-bit kernels already did), but evidently this was incorrect.

Always storing the dma_addr_t pointer as 64-bit little-endian,
i.e. initializing the second four bytes to zero in case of 32-bit
addressing, apparently solved the problem for Phil, and is consistent with
what all 64-bit little-endian machines did before.

I also checked in the history that in previous versions of the code, the
pointer was always in the first four bytes without padding, and that
previous attempts to fix 64-bit user space, big-endian architectures and
64-bit DMA were clearly flawed and seem to have introduced made this worse.

Link: https://lore.kernel.org/r/20210104234137.438275-1-arnd@kernel.org
Fixes: 381d34e3 ("scsi: megaraid_sas: Check user-provided offsets")
Fixes: 107a60dd ("scsi: megaraid_sas: Add support for 64bit consistent DMA")
Fixes: 94cd65dd ("[SCSI] megaraid_sas: addded support for big endian architecture")
Fixes: 7b2519af ("[SCSI] megaraid_sas: fix 64 bit sense pointer truncation")
Reported-by: Phil Oester <kernel@linuxace.com>
Tested-by: Phil Oester <kernel@linuxace.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>