From: David Hildenbrand <david@redhat.com>
To: Catalin Marinas <catalin.marinas@arm.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 12:38:31 +0200 [thread overview]
Message-ID: <b720e7c8-ca44-0a25-480b-05bf49d03c35@redhat.com> (raw)
In-Reply-To: <20210825102044.GA3420@arm.com>
On 25.08.21 12:20, Catalin Marinas wrote:
> + hch
>
> On Tue, Aug 24, 2021 at 08:59:22PM +0200, David Hildenbrand wrote:
>> On 24.08.21 20:46, Robin Murphy wrote:
>>> On 2021-08-24 19:28, Mike Rapoport wrote:
>>>> On Tue, Aug 24, 2021 at 06:37:41PM +0100, Catalin Marinas wrote:
>>>>> On Tue, Aug 24, 2021 at 03:40:47PM +0200, Alex Bee wrote:
>>>>>> it seems there is a regression in arm64 memory mapping in 5.14, since it
>>>>>> fails on Rockchip RK3328 when the pl330 dmac tries to map with:
>>>>>>
>>>>>> ------------[ cut here ]------------
>>>>>> WARNING: CPU: 2 PID: 373 at kernel/dma/mapping.c:235 dma_map_resource+0x68/0xc0
>>>>>> Modules linked in: spi_rockchip(+) fuse
>>>>>> CPU: 2 PID: 373 Comm: systemd-udevd Not tainted 5.14.0-rc7 #1
>>>>>> Hardware name: Pine64 Rock64 (DT)
>>>>>> pstate: 80000005 (Nzcv daif -PAN -UAO -TCO BTYPE=--)
>>>>>> pc : dma_map_resource+0x68/0xc0
>>>>>> lr : pl330_prep_slave_fifo+0x78/0xd0
>>>>>> sp : ffff800012102ae0
>>>>>> x29: ffff800012102ae0 x28: ffff000005c94800 x27: 0000000000000000
>>>>>> x26: ffff000000566bd0 x25: 0000000000000001 x24: 0000000000000001
>>>>>> x23: 0000000000000002 x22: ffff000000628c00 x21: 0000000000000001
>>>>>> x20: ffff000000566bd0 x19: 0000000000000001 x18: 0000000000000000
>>>>>> x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
>>>>>> x14: 0000000000000277 x13: 0000000000000001 x12: 0000000000000000
>>>>>> x11: 0000000000000001 x10: 00000000000008e0 x9 : ffff800012102a80
>>>>>> x8 : ffff000000d14b80 x7 : ffff0000fe7b12f0 x6 : ffff0000fe7b1100
>>>>>> x5 : fffffc000000000f x4 : 0000000000000000 x3 : 0000000000000001
>>>>>> x2 : 0000000000000001 x1 : 00000000ff190800 x0 : ffff000000628c00
>>>>>> Call trace:
>>>>>> dma_map_resource+0x68/0xc0
>>>>>> pl330_prep_slave_sg+0x58/0x220
>>>>>> rockchip_spi_prepare_dma+0xd8/0x2c0 [spi_rockchip]
>>>>>> rockchip_spi_transfer_one+0x294/0x3d8 [spi_rockchip]
>>>>> [...]
>>>>>> Note: This does not relate to the spi driver - when disabling this device in
>>>>>> the device tree it fails for any other (i2s, for instance) which uses dma.
>>>>>> Commenting out the failing check at [1], however, helps and the mapping
>>>>>> works again.
>>>>
>>>>> Do you know which address dma_map_resource() is trying to map (maybe
>>>>> add some printk())? It's not supposed to map RAM, hence the warning.
>>>>> Random guess, the address is 0xff190800 (based on the x1 above but the
>>>>> regs might as well be mangled).
>>>>
>>>> 0xff190800 will cause this warning for sure. It has a memory map, but it is
>>>> not RAM so old version of pfn_valid() would return 0 and the new one
>>>> returns 1.
>>>
>>> How does that happen, though? It's not a memory address, and it's not
>>> even within the bounds of anywhere there should or could be memory. This
>>> SoC has a simple memory map - everything from 0 to 0xfeffffff goes to
>>> the DRAM controller (which may not all be populated, and may have pieces
>>> carved out by secure firmware), while 0xff000000-0xffffffff is MMIO. Why
>>> do we have pages (or at least the assumption of pages) for somewhere
>>> which by all rights should not have them?
>>
>> Simple: we allocate the vmemmap for whole sections (e.g., 128 MiB) to avoid
>> any such hacks. If there is a memory hole, it gets a memmap as well.
>>
>> Tricking pfn_valid() into returning "false" where we actually have a memmap
>> only makes it look like there is no memmap; but there is one, and
>> it's PG_reserved.
>
> 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)
Would you expect to have a direct map for memory holes and similar (IOW,
!System RAM)?
>>>>> Either pfn_valid() gets confused in 5.14 or something is wrong with the
>>>>> DT. I have a suspicion it's the former since reverting the above commit
>>>>> makes it disappear.
>>>>
>>>> I think pfn_valid() actually behaves as expected but the caller is wrong
>>>> because pfn_valid != RAM (this applies btw to !arm64 as well).
>>>>
>>>> /* Don't allow RAM to be mapped */
>>>> if (WARN_ON_ONCE(pfn_valid(PHYS_PFN(phys_addr))))
>>>> return DMA_MAPPING_ERROR;
>>>>
>>>> Alex, can you please try this patch:
>>>
>>> That will certainly paper over the issue, but it's avoiding the question
>>> of what went wrong with the memory map in the first place. The comment
>>> is indeed a bit inaccurate, but ultimately dma_map_resource() exists for
>>> addresses that would be wrong to pass to dma_map_page(), so I believe
>>> pfn_valid() is still the correct check.
>>
>> If we want to check for RAM, pfn_valid() would be wrong. If we want to check
>> for "is there a memmap, for whatever lives or does not live there",
>> pfn_valid() is the right check.
>
> So what should the DMA code use instead? Last time we needed something
> similar, the recommendation was to use pfn_to_online_page(). Mike is
> suggesting memblock_is_memory().
We use pfn_to_online_page() when we want to know if it's system RAM and
that the memmap actually contains something sane (-> memmap content has
a well defined state).
You can have offline memory blocks where pfn_to_online_page() would
return "false", memblock_is_memory() would return "true". IOW, there is
a memmap, it's System RAM, but the memmap is stale and not trustworthy.
If you want to make sure no System RAM (online/offline/...) will get
mapped, memblock_is_memory() should be the right thing to use. I recall
that x86 traverse the resource tree instead to exclude system ram
regions similarly.
>
> Given how later we are in the -rc cycle, I suggest we revert Anshuman's
> commit 16c9afc77660 ("arm64/mm: drop HAVE_ARCH_PFN_VALID") and try to
> assess the implications in 5.15 (the patch doesn't seem to have the
> arm64 maintainers' ack anyway ;)).
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-08-25 10:38 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 [this message]
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
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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