RE: [PATCH v4] cxl/mbox: Fix Payload Length check for Get Log command

[Dan Williams <dan.j.williams@intel.com>]

Robert Richter wrote:
> Commit 2aeaf663b85e introduced strict checking for variable length
> payload size validation. The payload length of received data must
> match the size of the requested data by the caller except for the case
> where the min_out value is set.
> 
> The Get Log command does not have a header with a length field set.
> The Log size is determined by the Get Supported Logs command (CXL 3.0,
> 8.2.9.5.1). However, the actual size can be smaller and the number of
> valid bytes in the payload output must be determined reading the
> Payload Length field (CXL 3.0, Table 8-36, Note 2).
> 
> Two issues arise: The command can successfully complete with a payload
> length of zero. And, the valid payload length must then also be
> consumed by the caller.
> 
> Change cxl_xfer_log() to pass the number of payload bytes back to the
> caller to determine the number of log entries. Implement the payload
> handling as a special case where mbox_cmd->size_out is consulted when
> cxl_internal_send_cmd() returns -EIO. A WARN_ONCE() is added to check
> that -EIO is only returned in case of an unexpected output size.
> 
> Logs can be bigger than the maximum payload length and multiple Get
> Log commands can be issued. If the received payload size is smaller
> than the maximum payload size we can assume all valid bytes have been
> fetched. Stop sending further Get Log commands then.
> 
> On that occasion, change debug messages to also report the opcodes of
> supported commands.
> 
> The variable payload commands GET_LSA and SET_LSA are not affected by
> this strict check: SET_LSA cannot be broken because SET_LSA does not
> return an output payload, and GET_LSA never expects short reads.
> 
> Fixes: 2aeaf663b85e ("cxl/mbox: Add variable output size validation for internal commands")
> Signed-off-by: Robert Richter <rrichter@amd.com>
> ---
> v4:
>  * Fixed a build issue.
> v3:
>  * Added comment to the WARN_ONCE(). (Jonathan)
>  * Passing a size pointer to report the payload size back. (Jonathan)
>  * Moved logging of supported opcodes out of this patch for a separate
>    change. (Jonathan)
> 
>  drivers/cxl/core/mbox.c | 25 ++++++++++++++++++++++---
>  1 file changed, 22 insertions(+), 3 deletions(-)

Looks good Robert. Do you think this is v6.2-rc material or can it wait
for v6.3? It sounds like you have a real device that needs, so I am
inclined to add it to cxl/fixes for this cycle.