From: Catalin Marinas <catalin.marinas@arm.com>
To: Mike Rapoport <rppt@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>,
David Hildenbrand <david@redhat.com>,
Robin Murphy <robin.murphy@arm.com>,
Alex Bee <knaerzche@gmail.com>, Will Deacon <will@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [BUG 5.14] arm64/mm: dma memory mapping fails (in some cases)
Date: Mon, 20 Sep 2021 11:57:58 +0100 [thread overview]
Message-ID: <YUhpNgwwttW1ewez@arm.com> (raw)
In-Reply-To: <YUXQBV6KKi+/Q6gX@kernel.org>
On Sat, Sep 18, 2021 at 02:39:49PM +0300, Mike Rapoport wrote:
> On Sat, Sep 18, 2021 at 11:37:22AM +0300, Mike Rapoport wrote:
> > On Sat, Sep 18, 2021 at 07:18:43AM +0200, Christoph Hellwig wrote:
> > > On Sat, Sep 18, 2021 at 12:22:47AM +0300, Mike Rapoport wrote:
> > > > I did some digging and it seems that the most "generic" way to check if a
> > > > page is in RAM is page_is_ram(). It's not 100% bullet proof as it'll give
> > > > false negatives for architectures that do not register "System RAM", but
> > > > those are not using dma_map_resource() anyway and, apparently, never would.
> > >
> > > The downside of page_is_ram is that it looks really expensiv for
> > > something done at dma mapping time.
> >
> > Indeed :(
> > But pfn_valid is plain wrong...
> > I'll keep digging.
>
> I did some more archaeology and it that check for pfn_valid() was requested
> by arm folks because their MMU may have troubles with alias mappings with
> different attributes and so they made the check to use a false assumption
> that pfn_valid() == "RAM".
>
> As this WARN_ON(pfn_valid()) is only present in dma_map_resource() it's
> probably safe to drop it entirely.
I agree, we should drop it. IIUC dma_map_resource() does not create any
kernel mapping to cause problems with attribute aliasing. You'd need a
prior devm_ioremap_resource() if you want access to that range from the
CPU side. For arm64 at least, the latter ends up with a
pfn_is_map_memory() check.
--
Catalin
next prev parent reply other threads:[~2021-09-20 10:58 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-24 13:40 [BUG 5.14] arm64/mm: dma memory mapping fails (in some cases) Alex Bee
2021-08-24 17:37 ` Catalin Marinas
2021-08-24 18:06 ` Robin Murphy
2021-08-24 18:28 ` Mike Rapoport
2021-08-24 18:46 ` Robin Murphy
2021-08-24 18:59 ` David Hildenbrand
2021-08-25 10:20 ` Catalin Marinas
2021-08-25 10:28 ` Will Deacon
2021-08-25 10:32 ` Will Deacon
2021-08-25 10:33 ` Robin Murphy
2021-08-25 10:38 ` David Hildenbrand
2021-08-25 10:54 ` Mike Rapoport
2021-08-25 10:55 ` Catalin Marinas
2021-08-25 11:12 ` David Hildenbrand
2021-08-25 17:15 ` Catalin Marinas
2021-08-25 10:58 ` Robin Murphy
2021-08-25 11:21 ` David Hildenbrand
2021-08-25 10:52 ` Mike Rapoport
2021-09-17 21:22 ` Mike Rapoport
2021-09-18 5:18 ` Christoph Hellwig
2021-09-18 8:37 ` Mike Rapoport
2021-09-18 11:39 ` Mike Rapoport
2021-09-20 10:57 ` Catalin Marinas [this message]
2021-09-21 8:20 ` Christoph Hellwig
2021-09-21 9:34 ` Mike Rapoport
2021-09-21 15:38 ` Christoph Hellwig
2021-09-22 7:22 ` Mike Rapoport
2021-09-20 11:13 ` David Hildenbrand
2021-08-24 20:14 ` Alex Bee
2021-08-25 4:39 ` Mike Rapoport
2021-08-25 10:00 ` Alex Bee
2021-08-24 20:07 ` Alex Bee
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