Re: [PATCH v7 1/1] vfio/nvgpu: Add vfio pci variant module for grace hopper

[Jason Gunthorpe]

On Wed, Aug 23, 2023 at 09:14:07AM -0600, Alex Williamson wrote:
> On Wed, 23 Aug 2023 14:50:31 +0000
> Ankit Agrawal <ankita@xxxxxxxxxx> wrote:
> 
> > >> +     if (index == VFIO_PCI_BAR2_REGION_INDEX) {
> > >> +             if (!nvdev->opregion) {
> > >> +                     nvdev->opregion = memremap(nvdev->hpa, nvdev->mem_length, MEMREMAP_WB);
> > >> +                     if (!nvdev->opregion)
> > >> +                             return -ENOMEM;
> > >> +             }  
> > >
> > > [AW] Seems like this would be susceptible to concurrent accesses causing
> > > duplicate mappings.
> > >
> > > [JG] Needs some kind of locking on opregion  
> > 
> > Right, will add a new lock item in nvdev to control the access to opregion/memmap.
> > Please let me know if it is preferable to do memremap in open_device instead of
> > read/write.
> 
> That's a valid option also, certainly avoids the locking and
> serialization per access.  Thanks,

open_device is no good, that would waste large amounts of kernel
memory for page tables to support something we don't expect to be
used.

Jason