Re: [PATCH v3 12/16] PCI: Obey iomem restrictions for procfs mmap

[Jason Gunthorpe]

On Wed, Oct 21, 2020 at 05:54:54PM +0200, Daniel Vetter wrote:

> The trouble is that io_remap_pfn adjust vma->pgoff, so we'd need to
> split that. So ideally ->mmap would never set up any ptes.

/dev/mem makes pgoff == pfn so it doesn't get changed by remap.

pgoff doesn't get touched for MAP_SHARED either, so there are other
users that could work like this - eg anyone mmaping IO memory is
probably OK.

> I guess one option would be if remap_pfn_range would steal the
> vma->vm_ops pointer for itself, then it could set up the correct
> ->install_ptes hook. But there's tons of callers for that, so not sure
> that's a bright idea.

The caller has to check that the mapping is still live, and I think
hold a lock across the remap? Auto-defering it doesn't seem feasible.

Jason