Re: [PATCH v17 3/3] vfio/nvgrace-gpu: Add vfio pci variant module for grace hopper

[Alex Williamson]

On Fri, 9 Feb 2024 13:19:03 -0400
Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:

> On Fri, Feb 09, 2024 at 08:55:31AM -0700, Alex Williamson wrote:
> > I think Kevin's point is also relative to this latter scenario, in the
> > L1 instance of the nvgrace-gpu driver the mmap of the usemem BAR is
> > cachable, but in the L2 instance of the driver where we only use the
> > vfio-pci-core ops nothing maintains that cachable mapping.  Is that a
> > problem?  An uncached mapping on top of a cachable mapping is often
> > prone to problems.    
> 
> On these CPUs the ARM architecture won't permit it, the L0 level
> blocks uncachable using FWB and page table attributes. The VM, no
> matter what it does, cannot make the cachable memory uncachable.

Great, thanks,

Alex