Re: [PATCH v3 2/3] vfio/nvgrace-gpu: Expose the blackwell device PF BAR1 to the VM

[Ankit Agrawal]

>> +     if (!nvdev->has_mig_hw_bug_fix) {
>> +             /*
>> +              * If the device memory is split to workaround the MIG bug,
>> +              * the USEMEM part of the device memory has to be MEMBLK_SIZE
>> +              * aligned. This is a hardwired ABI value between the GPU FW and
>> +              * VFIO driver. The VM device driver is also aware of it and make
>> +              * use of the value for its calculation to determine USEMEM size.
>> +              *
>> +              * If the hardware has the fix for MIG, there is no requirement
>> +              * for splitting the device memory to create RESMEM. The entire
>> +              * device memory is usable and will be USEMEM.
>> +              */
>> +             nvdev->usemem.memlength = round_down(nvdev->usemem.memlength,
>> +                                                  MEMBLK_SIZE);
>> +             if (nvdev->usemem.memlength == 0) {
>> +                     ret = -EINVAL;
>> +                     goto done;
>> +             }
>
> Why does this operation need to be predicated on the buggy device?
> Does GB have memory that's not a multiple of 512MB?  I was expecting
> this would be a no-op on GB and therefore wouldn't need to be
> conditional.  Thanks,
> 
> Alex

Thanks Alex, yeah the device memory size is not necessarily 512M aligned.