Re: [PATCH v11 1/1] vfio/nvgpu: Add vfio pci variant module for grace hopper

Alex Williamson
2023-10-09T19:37:25Z

On Sun, 8 Oct 2023 07:06:41 +0700
Bagas Sanjaya <bagasdotme@gmail.com> wrote:

> On Sun, Oct 08, 2023 at 01:52:54AM +0530, ankita@nvidia.com wrote:
> > PCI BAR are aligned to the power-of-2, but the actual memory on the
> > device may not. A read or write access to the physical address from the
> > last device PFN up to the next power-of-2 aligned physical address
> > results in reading ~0 and dropped writes.
> >
>
> Reading garbage or padding in that case?
>
> Confused...

The coherent memory size is rounded to a power-of-2 to be compliant with
PCI BAR semantics, but reading beyond the implemented size fills the
return buffer with -1 data, as is common on many platforms when reading
from an unimplemented section of the address space. Thanks,

Alex