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Date: Wed, 7 Oct 2020 14:33:23 -0300
From: Jason Gunthorpe <jgg@ziepe.ca>
Subject: Re: [PATCH 05/13] mm/frame-vector: Use FOLL_LONGTERM
Message-ID: <20201007173323.GV5177@ziepe.ca>
References: <20201007164426.1812530-1-daniel.vetter@ffwll.ch>
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 <20201007165316.GT5177@ziepe.ca>
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To: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: DRI Development <dri-devel@lists.freedesktop.org>, LKML <linux-kernel@vger.kernel.org>, kvm@vger.kernel.org, Linux MM <linux-mm@kvack.org>, Linux ARM <linux-arm-kernel@lists.infradead.org>, linux-samsung-soc <linux-samsung-soc@vger.kernel.org>, "open list:DMA BUFFER SHARING FRAMEWORK" <linux-media@vger.kernel.org>, linux-s390@vger.kernel.org, Daniel Vetter <daniel.vetter@intel.com>, Pawel Osciak <pawel@osciak.com>, Marek Szyprowski <m.szyprowski@samsung.com>, Kyungmin Park <kyungmin.park@samsung.com>, Tomasz Figa <tfiga@chromium.org>, Mauro Carvalho Chehab <mchehab@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, John Hubbard <jhubbard@nvidia.com>, =?utf-8?B?SsOpcsO0bWU=?= Glisse <jglisse@redhat.com>, Jan Kara <jack@suse.cz>, Dan Williams <dan.j.williams@intel.com>

On Wed, Oct 07, 2020 at 07:12:24PM +0200, Daniel Vetter wrote:
> On Wed, Oct 7, 2020 at 6:53 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> >
> > On Wed, Oct 07, 2020 at 06:44:18PM +0200, Daniel Vetter wrote:
> > >
> > > -     /*
> > > -      * While get_vaddr_frames() could be used for transient (kernel
> > > -      * controlled lifetime) pinning of memory pages all current
> > > -      * users establish long term (userspace controlled lifetime)
> > > -      * page pinning. Treat get_vaddr_frames() like
> > > -      * get_user_pages_longterm() and disallow it for filesystem-dax
> > > -      * mappings.
> > > -      */
> > > -     if (vma_is_fsdax(vma)) {
> > > -             ret = -EOPNOTSUPP;
> > > -             goto out;
> > > -     }
> > > -
> > > -     if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
> > > -             vec->got_ref = true;
> > > -             vec->is_pfns = false;
> > > -             ret = pin_user_pages_locked(start, nr_frames,
> > > -                     gup_flags, (struct page **)(vec->ptrs), &locked);
> > > -             goto out;
> > > -     }
> >
> > The vm_flags still need to be checked before going into the while
> > loop. If the break is taken then nothing would check vm_flags
> 
> Hm right that's a bin inconsistent. follow_pfn also checks for this,
> so I think we can just ditch this entirely both here and in the do {}
> while () check, simplifying the latter to just while (vma). Well, just
> make it a real loop with less confusing control flow probably.

It does read very poorly with the redundant check, espeically since I
keep forgetting follow_pfn does it too :\

Jason