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From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: Christoph Hellwig <hch@infradead.org>
Cc: DRI Development <dri-devel@lists.freedesktop.org>,
	LKML <linux-kernel@vger.kernel.org>,
	KVM list <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 <linux-s390@vger.kernel.org>
Subject: Re: [PATCH v4 00/15] follow_pfn and other iomap races
Date: Thu, 29 Oct 2020 10:38:16 +0100
Message-ID: <CAKMK7uG=R2372bVTK1Zh+P7uRd2QJSw5EgcJ6JJwVtNyJ7SJtQ@mail.gmail.com> (raw)
In-Reply-To: <20201029092800.GA494@infradead.org>

On Thu, Oct 29, 2020 at 10:28 AM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Thu, Oct 29, 2020 at 10:25:16AM +0100, Daniel Vetter wrote:
> > On Thu, Oct 29, 2020 at 9:57 AM Christoph Hellwig <hch@infradead.org> wrote:
> > >
> > > Maybe I'm missing something, but shouldn't follow_pfn be unexported
> > > at the end of the series?
> >
> > kvm is a legit user and modular afaict. But since you can't use this
> > without an mmu_notifier anyway (or digging around in pagetable
> > locking), maybe it should be EXPORT_SYMBOL_GPL now at least?
>
> I think it should then take the notifier as an argument even if it isn't
> diretly used as a safety check, and get a new name describing it.

Hm so Jason and me discussed this, but e.g. the s390 is safe with with
just the pagetable locks. So we'd need two versions.

The more practical problem is that I haven't found a reasonable way to
check that a passed in mmu_notifier is registered against the mm we're
working on, and without that check it feels a bit silly. But if you
see how to do that I think we can do an EXPORT_SYMBOL_GPL follow_pfn
which takes the notifier, and an __follow_pfn for s390 and similar
internal code which isn't exported.

> EXPORT_SYMBOL_GPL is probably ok for now, but I'm drafting a new
> EXPORT_SYMBOL_FOR_MODULE() which will export symbols that can only be
> used by one specific module, with kvm being a prime user due to all
> the odd exports it requires that aren't really the kernel interface by
> any normal means.

Hm yeah that's another one. There's also some virt stuff that's
currently on unsafe_follow_pfn and needs to be switched over, and I
think that would also need an mmu notifier of some sorts to close the
gaps.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

  reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-26 10:58 Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 01/15] drm/exynos: Stop using frame_vector helpers Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 02/15] drm/exynos: Use FOLL_LONGTERM for g2d cmdlists Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 03/15] misc/habana: Stop using frame_vector helpers Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 04/15] misc/habana: Use FOLL_LONGTERM for userptr Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 05/15] mm/frame-vector: Use FOLL_LONGTERM Daniel Vetter
2020-10-26 22:15   ` Tomasz Figa
2020-10-27  8:05     ` Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 06/15] media: videobuf2: Move frame_vector into media subsystem Daniel Vetter
2020-10-26 22:03   ` Tomasz Figa
2020-10-26 10:58 ` [PATCH v4 07/15] mm: Close race in generic_access_phys Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 08/15] mm: Add unsafe_follow_pfn Daniel Vetter
2020-10-29  8:56   ` Christoph Hellwig
2020-10-29  9:23     ` Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 09/15] media/videbuf1|2: Mark follow_pfn usage as unsafe Daniel Vetter
2020-10-26 22:02   ` Tomasz Figa
2020-10-26 10:58 ` [PATCH v4 10/15] vfio/type1: Mark follow_pfn " Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 11/15] PCI: Obey iomem restrictions for procfs mmap Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 12/15] /dev/mem: Only set filp->f_mapping Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 13/15] resource: Move devmem revoke code to resource framework Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 14/15] sysfs: Support zapping of binary attr mmaps Daniel Vetter
2020-10-26 10:58 ` [PATCH v4 15/15] PCI: Revoke mappings like devmem Daniel Vetter
2020-10-29  8:57 ` [PATCH v4 00/15] follow_pfn and other iomap races Christoph Hellwig
2020-10-29  9:25   ` Daniel Vetter
2020-10-29  9:28     ` Christoph Hellwig
2020-10-29  9:38       ` Daniel Vetter [this message]
2020-10-29 10:01         ` Christoph Hellwig

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