Re: [RFC PATCH 2/2] mm,drm/ttm: Use VM_PFNMAP for TTM vmas

[Jason Gunthorpe]

On Tue, Mar 23, 2021 at 04:46:00PM +0100, Thomas Hellström (Intel) wrote:
> > > +static inline bool is_cow_mapping(vm_flags_t flags)
> > > +{
> > > +	return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
> > > +}
> > Most driver places are just banning VM_SHARED.
> > 
> > I see you copied this from remap_pfn_range(), but that logic is so
> > special I'm not sure..
> 
> It's actually used all over the place. Both in drivers and also redefined
> with
> CONFIG_MEM_SOFT_DIRTY which makes me think Daniels idea of
> vma_is_cow_mapping() is better since it won't clash and cause compilation
> failures...

Well, lets update more mmap fops to use this new helper then?
Searching for VM_SHARED gives a good list, there are several in
drivers/infiniband

Jason