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Date:   Tue, 23 Mar 2021 13:06:14 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Thomas =?utf-8?B?SGVsbHN0csO2bSAoSW50ZWwp?= 
        <thomas_os@shipmail.org>
Cc:     dri-devel@lists.freedesktop.org,
        Christian Koenig <christian.koenig@amd.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 2/2] mm,drm/ttm: Use VM_PFNMAP for TTM vmas
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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