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

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 23 Aug 2023 12:16:23 -0300
Jason Gunthorpe <jgg@nvidia.com> wrote:

> 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@nvidia.com> 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.

A lock it is then, I guess this is a very large range of memory.  The
contention/serialization is also not a priority, we expect access
through the mmap for anything other than debug.  Thanks,

Alex