From: Catalin Marinas <catalin.marinas@arm.com>
To: David Hildenbrand <david@redhat.com>
Cc: Robin Murphy <robin.murphy@arm.com>,
Mike Rapoport <rppt@kernel.org>, 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>,
Christoph Hellwig <hch@lst.de>
Subject: Re: [BUG 5.14] arm64/mm: dma memory mapping fails (in some cases)
Date: Wed, 25 Aug 2021 18:15:53 +0100 [thread overview]
Message-ID: <20210825171552.GH3420@arm.com> (raw)
In-Reply-To: <547785ff-e02f-df28-7f9c-9ad4f5b3cc77@redhat.com>
On Wed, Aug 25, 2021 at 01:12:37PM +0200, David Hildenbrand wrote:
> On 25.08.21 12:55, Catalin Marinas wrote:
> > On Wed, Aug 25, 2021 at 12:38:31PM +0200, David Hildenbrand wrote:
> > > On 25.08.21 12:20, Catalin Marinas wrote:
> > > > I can see the documentation for pfn_valid() does not claim anything more
> > > > than the presence of an memmap entry. But I wonder whether the confusion
> > > > is wider-spread than just the DMA code. At a quick grep, try_ram_remap()
> > > > assumes __va() can be used on pfn_valid(), though I suspect it relies on
> > > > the calling function to check that the resource was RAM. The arm64
> > > > kern_addr_valid() returns true based on pfn_valid() and kcore.c uses
> > > > standard memcpy on it, which wouldn't work for I/O (should we change
> > > > this check to pfn_is_map_memory() for arm64?).
> > >
> > > kern_addr_valid() checks that there is a direct map entry, and that the
> > > mapped address has a valid mmap. (copied from x86-64)
> >
> > It checks that there is a va->pa mapping, not necessarily in the linear
> > map as it walks the page tables. So for some I/O range that happens to
> > be mapped but which was in close proximity to RAM so that pfn_valid() is
> > true, kern_addr_valid() would return true. I don't thin that was the
> > intention.
> >
> > > Would you expect to have a direct map for memory holes and similar (IOW,
> > > !System RAM)?
> >
> > No, but we with the generic pfn_valid(), it may return true for mapped
> > MMIO (with different attributes than the direct map).
>
> Ah, right. But can we actually run into that via kcore?
>
> kcore builds the RAM list via walk_system_ram_range(), IOW the resource
> tree. And we end up calling kern_addr_valid() only on KCORE_RAM,
> KCORE_VMEMMAP and KCORE_TEXT.
It's probably fine but I'd rather do some check of the other call sites
before attempting to move arm64 to the generic pfn_valid() again.
--
Catalin
next prev parent reply other threads:[~2021-08-25 17:15 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 [this message]
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
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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