From: Lukas Wunner <lukas@wunner•de>
To: Gerd Bayer <gbayer@linux•ibm.com>
Cc: 18255117159@163•com, bhelgaas@google•com, helgaas@kernel•org,
agordeev@linux•ibm.com, borntraeger@linux•ibm.com,
ilpo.jarvinen@linux•intel.com, jingoohan1@gmail•com,
kwilczynski@kernel•org, linux-kernel@vger•kernel.org,
linux-s390@vger•kernel.org, linux-next@vger•kernel.org,
linux-pci@vger•kernel.org, lpieralisi@kernel•org,
mani@kernel•org, robh@kernel•org, schnelle@linux•ibm.com
Subject: Re: [PATCH] PCI: Fix endianness issues in pci_bus_read_config()
Date: Thu, 31 Jul 2025 20:53:44 +0200 [thread overview]
Message-ID: <aIu7uO4NOanxMfAO@wunner.de> (raw)
In-Reply-To: <20250731173858.1173442-1-gbayer@linux.ibm.com>
On Thu, Jul 31, 2025 at 07:38:58PM +0200, Gerd Bayer wrote:
> Simple pointer-casts to map byte and word reads from PCI config space
> into dwords (i.e. u32) produce unintended results on big-endian systems.
> Add the necessary adjustments under compile-time switch
> CONFIG_CPU_BIG_ENDIAN.
>
> pci_bus_read_config() was just introduced with
> https://lore.kernel.org/all/20250716161203.83823-2-18255117159@163.com/
>
> Signed-off-by: Gerd Bayer <gbayer@linux•ibm.com>
> ---
> Sorry to spill this endianness aware code into drivers/pci, feel free to
> suggest a cleaner approach. This has fixed the issues seen on s390 systems
PCI is little-endian. On big-endian systems, the endianness conversion
of Config Space accesses happens transparently in the struct pci_ops
->read() and ->write() callbacks. E.g. on s390, zpci_cfg_load() and
zpci_cfg_store() call le64_to_cpu() and cpu_to_le64(), respectively.
We do not want to mess with endianness in the PCI core, so this isn't
a proper fix IMO.
A viable approach might be to turn pci_bus_read_config() into a macro
in include/linux/pci.h which calls the byte/word/dword variant based
on sizeof(*val) or something like that.
But at this point, with the merge window already open, it's probably
better to drop the pci/capability-search topic branch from the pull
request and retry in the next cycle.
> Since this is still sitting in the a pull-request for upstream,
> I'm not sure if this warrants a Fixes: tag.
In cases like this, do include a Fixes tag but no stable designation.
Thanks,
Lukas
next prev parent reply other threads:[~2025-07-31 18:53 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20250716231121.GA2564572@bhelgaas>
2025-07-31 7:32 ` [REGRESSION] next/master: suspect endianness issue in common PCI capability search macro Gerd Bayer
2025-07-31 17:38 ` [PATCH] PCI: Fix endianness issues in pci_bus_read_config() Gerd Bayer
2025-07-31 18:39 ` Bjorn Helgaas
2025-07-31 19:01 ` Arnd Bergmann
2025-08-01 8:18 ` Manivannan Sadhasivam
2025-08-01 9:25 ` Hans Zhang
2025-08-01 9:47 ` Manivannan Sadhasivam
2025-08-01 10:06 ` Hans Zhang
2025-08-01 10:54 ` Manivannan Sadhasivam
2025-08-01 11:30 ` Gerd Bayer
2025-08-01 16:54 ` Hans Zhang
2025-08-01 18:08 ` Keith Busch
2025-08-02 15:23 ` Hans Zhang
2025-08-02 15:40 ` Arnd Bergmann
2025-08-04 3:06 ` Hans Zhang
2025-08-04 8:03 ` Arnd Bergmann
2025-08-04 8:25 ` Hans Zhang
2025-08-04 10:09 ` Gerd Bayer
2025-08-12 14:44 ` Hans Zhang
2025-08-13 7:47 ` Niklas Schnelle
2025-08-13 7:50 ` Hans Zhang
2025-08-04 14:33 ` Bjorn Helgaas
2025-08-04 15:04 ` Hans Zhang
2025-08-01 16:47 ` Hans Zhang
2025-07-31 18:53 ` Lukas Wunner [this message]
2025-08-01 7:52 ` Geert Uytterhoeven
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=aIu7uO4NOanxMfAO@wunner.de \
--to=lukas@wunner$(echo .)de \
--cc=18255117159@163$(echo .)com \
--cc=agordeev@linux$(echo .)ibm.com \
--cc=bhelgaas@google$(echo .)com \
--cc=borntraeger@linux$(echo .)ibm.com \
--cc=gbayer@linux$(echo .)ibm.com \
--cc=helgaas@kernel$(echo .)org \
--cc=ilpo.jarvinen@linux$(echo .)intel.com \
--cc=jingoohan1@gmail$(echo .)com \
--cc=kwilczynski@kernel$(echo .)org \
--cc=linux-kernel@vger$(echo .)kernel.org \
--cc=linux-next@vger$(echo .)kernel.org \
--cc=linux-pci@vger$(echo .)kernel.org \
--cc=linux-s390@vger$(echo .)kernel.org \
--cc=lpieralisi@kernel$(echo .)org \
--cc=mani@kernel$(echo .)org \
--cc=robh@kernel$(echo .)org \
--cc=schnelle@linux$(echo .)ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
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