From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: Florian Weimer <fweimer@redhat.com>,
Andrew Pinski <pinskia@gmail.com>,
Richard Earnshaw <Richard.Earnshaw@arm.com>,
Ramana Radhakrishnan <ramana.gcc@googlemail.com>,
Thomas Petazzoni <thomas.petazzoni@free-electrons.com>,
GNU C Library <libc-alpha@sourceware.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Russell King <linux@armlinux.org.uk>,
LKML <linux-kernel@vger.kernel.org>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: framebuffer corruption due to overlapping stp instructions on arm64
Date: Mon, 6 Aug 2018 12:37:26 +0200 [thread overview]
Message-ID: <CAKv+Gu87YqLM=FFZ6V8rHhuhskDdsBUuXFpqNKVbXWqdnuNEyA@mail.gmail.com> (raw)
In-Reply-To: <alpine.LRH.2.02.1808060626060.2986@file01.intranet.prod.int.rdu2.redhat.com>
On 6 August 2018 at 12:31, Mikulas Patocka <mpatocka@redhat.com> wrote:
>
>
> On Mon, 6 Aug 2018, Ard Biesheuvel wrote:
>
>> On 6 August 2018 at 10:02, Mikulas Patocka <mpatocka@redhat.com> wrote:
>> >
>> >
>> > On Sun, 5 Aug 2018, Florian Weimer wrote:
>> >
>> >> On 08/04/2018 01:04 PM, Mikulas Patocka wrote:
>> >> > There's plenty of memcpy's in the graphics stack. No one will be rewriting
>> >> > all the graphics drivers because of tiny market share that ARM has in
>> >> > desktop computers. So if you refuse to fix things and blame everyone else,
>> >> > you can as well announce that you don't want to have PCIe graphics on ARM
>> >> > at all.
>> >>
>> >> The POWER toolchain maintainers said pretty much the same thing not too
>> >> long ago. I wonder how many architectures need to fail until the
>> >> graphics stack is finally fixed.
>> >>
>> >> Thanks,
>> >> Florian
>> >
>> > If you say that your architecture doesn't support unaligned accesses at
>> > all, there's no problem - the compiler won't generate them and the libc
>> > won't contain them.
>> >
>> > But if you say that your architecture supports unaligned accesses except
>> > for the framebuffer, then you have a problem - the compiler can't know
>> > which pointers point to the framebuffer and libc can't know either - you
>> > caused this problem by your architectural decision.
>> >
>> > You can use 'volatile' to suppress memory optimizations, but it's
>> > impossible to go through the whole Linux graphics stack and add volatile
>> > to every pointer that may point to videoram. Even if you succeesed, new
>> > videoram accesses without volatile will appear after a year of
>> > development.
>> >
>> > See for example the macros READ_ONCE and WRITE_ONCE in Linux kernel - they
>> > should be used when there's concurrent access to the particular variable,
>> > but mainstream architectures don't require them, so many kernel developers
>> > are omitting them in their code.
>> >
>> > If you are building a supercomputer with a particular GPU, you can force
>> > the GPU vendor to provide POWER-compliant drivers. If you are building a
>> > workstation where the user can plug any GPU, forcing developers will go
>> > nowhere. You have to emulate the unaligned accesses and make sure that the
>> > next versions of your architecture support them in hardware.
>> >
>>
>> I have the feeling this discussion is going off the rails again.
>>
>> The original report is about corruption when doing overlapping writes.
>> Matt Sealey said you cannot have PCI outbound windows with memory
>> semantics on ARM, and so you should be using device mappings (which do
>> not tolerate unaligned accesses)
>>
>> In this context, 'device mapping' does not mean 'any non-DRAM region',
>> but it refers to a particular type of MMU mapping attribute defined by
>> the ARM architecture.
>>
>> I think we can all agree that memcpy() should be usable on any region
>> of memory that has true memory semantics, even if it is backed by VRAM
>> on a graphics card.
>>
>> The question is if PCIe can provide such regions on ARM.
>
> I think there are three possible solutions:
>
> 1. provide an alternative memcpy implementation that doesn't do unaligned
> accesses and recompile the graphics software with -mstrict-align
>
> 2. map the PCI BAR as device memory and emulate the unaligned instructions
>
> 3. find some hardware workaround that could insert delays between the PCIe
> accesses (but the hardware engineers need to cooperate on this instead of
> asserting that they refuse tu support it)
>
Are we talking about a quirk for the Armada 8040 or about PCIe on ARM
in general?
If the latter, I still haven't seen an explanation why the particulars
of AMBA justify overlapped writes being dropped at will by the
interconnect.
next prev parent reply other threads:[~2018-08-06 10:37 UTC|newest]
Thread overview: 95+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-02 19:31 framebuffer corruption due to overlapping stp instructions on arm64 Mikulas Patocka
[not found] ` <CAHCPf3tFGqkYEcWNN4LaWThw_rVqT316pzLv6T7RfxwO-eZ0EA@mail.gmail.com>
2018-08-03 6:35 ` Mikulas Patocka
2018-08-03 7:16 ` Ard Biesheuvel
2018-08-03 9:41 ` Will Deacon
2018-08-03 17:09 ` Mikulas Patocka
2018-08-03 17:32 ` Sinan Kaya
2018-08-03 17:33 ` Ard Biesheuvel
2018-08-03 18:25 ` Mikulas Patocka
2018-08-03 20:44 ` Matt Sealey
2018-08-03 21:20 ` Ard Biesheuvel
2018-08-06 10:25 ` Mikulas Patocka
2018-08-06 12:42 ` Robin Murphy
2018-08-06 12:53 ` Ard Biesheuvel
2018-08-06 13:41 ` Marcin Wojtas
2018-08-06 13:48 ` Ard Biesheuvel
2018-08-06 14:07 ` Marcin Wojtas
2018-08-06 14:13 ` Mikulas Patocka
2018-08-06 15:47 ` Ard Biesheuvel
2018-08-06 17:09 ` Mikulas Patocka
2018-08-06 17:21 ` Ard Biesheuvel
2018-08-06 19:54 ` Mikulas Patocka
2018-08-06 20:11 ` Ard Biesheuvel
2018-08-06 20:31 ` Mikulas Patocka
2018-08-07 16:40 ` Marcin Wojtas
2018-08-07 17:39 ` Mikulas Patocka
2018-08-07 18:07 ` Ard Biesheuvel
2018-08-07 18:17 ` Mikulas Patocka
[not found] ` <CAPv3WKcKoEe=Qysp6Oac2C=G9bUhUQf1twSRCY+_qJ6XEC-iag@mail.gmail.com>
2018-08-08 14:10 ` Mikulas Patocka
2018-08-06 17:13 ` Catalin Marinas
2018-08-06 17:19 ` Mikulas Patocka
2018-08-08 18:31 ` Mikulas Patocka
2018-08-04 13:29 ` Mikulas Patocka
2018-08-08 12:16 ` Catalin Marinas
2018-08-08 13:02 ` David Laight
2018-08-08 13:46 ` Mikulas Patocka
2018-08-08 14:26 ` David Laight
2018-08-08 14:50 ` Catalin Marinas
2018-08-08 16:21 ` Mikulas Patocka
2018-08-08 16:31 ` Arnd Bergmann
2018-08-08 16:43 ` David Laight
2018-08-08 18:56 ` Mikulas Patocka
2018-08-08 18:37 ` Mikulas Patocka
2018-08-08 11:39 ` Catalin Marinas
2018-08-08 14:12 ` Mikulas Patocka
2018-08-08 14:28 ` Catalin Marinas
2018-08-08 18:40 ` Mikulas Patocka
2018-08-08 15:01 ` Richard Earnshaw (lists)
2018-08-08 15:14 ` Catalin Marinas
2018-08-08 16:01 ` Arnd Bergmann
2018-08-08 18:25 ` Mikulas Patocka
2018-08-08 21:51 ` Arnd Bergmann
2018-08-09 15:29 ` Arnd Bergmann
2018-08-03 7:11 ` Andrew Pinski
2018-08-03 7:53 ` Florian Weimer
2018-08-03 9:12 ` Szabolcs Nagy
2018-08-03 9:15 ` Ramana Radhakrishnan
2018-08-03 9:29 ` Ard Biesheuvel
2018-08-03 9:37 ` Ramana Radhakrishnan
2018-08-03 9:42 ` Richard Earnshaw (lists)
2018-08-04 0:58 ` Mikulas Patocka
2018-08-04 1:13 ` Andrew Pinski
2018-08-04 11:04 ` Mikulas Patocka
2018-08-05 18:33 ` Florian Weimer
2018-08-06 8:02 ` Mikulas Patocka
2018-08-06 8:10 ` Ard Biesheuvel
2018-08-06 10:31 ` Mikulas Patocka
2018-08-06 10:37 ` Ard Biesheuvel [this message]
2018-08-06 10:42 ` Mikulas Patocka
2018-08-06 10:48 ` Ard Biesheuvel
2018-08-06 12:09 ` Mikulas Patocka
2018-08-06 12:19 ` Ard Biesheuvel
2018-08-06 12:22 ` Ard Biesheuvel
2018-08-07 14:14 ` Mikulas Patocka
2018-08-07 14:40 ` Ard Biesheuvel
2018-08-08 19:15 ` Mikulas Patocka
2018-08-06 11:19 ` Siddhesh Poyarekar
2018-08-06 11:29 ` Ard Biesheuvel
2018-08-06 14:26 ` Tulio Magno Quites Machado Filho
2018-08-05 21:51 ` Pavel Machek
2018-08-06 14:30 ` Mikulas Patocka
2018-08-03 11:24 ` David Laight
2018-08-03 12:04 ` Mikulas Patocka
2018-08-03 13:04 ` David Laight
2018-08-05 14:36 ` Mikulas Patocka
2018-08-06 10:18 ` David Laight
2018-08-07 14:07 ` Mikulas Patocka
2018-08-07 14:33 ` David Laight
2018-08-08 14:21 ` Mikulas Patocka
2018-08-03 13:20 ` Mikulas Patocka
2018-08-03 13:31 ` Mikulas Patocka
2018-08-03 14:17 ` Richard Earnshaw (lists)
2018-08-05 21:36 ` Pavel Machek
2018-08-06 8:04 ` Ramana Radhakrishnan
2018-08-06 8:44 ` Pavel Machek
2018-08-06 9:11 ` Ard Biesheuvel
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAKv+Gu87YqLM=FFZ6V8rHhuhskDdsBUuXFpqNKVbXWqdnuNEyA@mail.gmail.com' \
--to=ard.biesheuvel@linaro.org \
--cc=Richard.Earnshaw@arm.com \
--cc=catalin.marinas@arm.com \
--cc=fweimer@redhat.com \
--cc=libc-alpha@sourceware.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@armlinux.org.uk \
--cc=mpatocka@redhat.com \
--cc=pinskia@gmail.com \
--cc=ramana.gcc@googlemail.com \
--cc=thomas.petazzoni@free-electrons.com \
--cc=will.deacon@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).