From: Christoph Hellwig <hch@lst.de>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: LEROY Christophe <christophe.leroy2@cs-soprasteria.com>,
Christoph Hellwig <hch@lst.de>,
Christian Lamparter <christian.lamparter@isd.uni-stuttgart.de>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
Stan Johnson <userm57@yahoo.com>,
Finn Thain <fthain@linux-m68k.org>
Subject: Re: [PATCH v2] powerpc: warn on emulation of dcbz instruction in kernel mode
Date: Fri, 23 Aug 2024 15:54:59 +0200 [thread overview]
Message-ID: <20240823135459.GA28487@lst.de> (raw)
In-Reply-To: <20240823130600.GI28254@gate.crashing.org>
On Fri, Aug 23, 2024 at 08:06:00AM -0500, Segher Boessenkool wrote:
> What does "uncached memory" even mean here? Literally it would be
> I=1 memory (uncachEABLE memory), but more likely you want M=0 memory
> here ("non-memory memory", "not well-behaved memory", MMIO often).
Regular kernel memory vmapped with pgprot_noncached().
> If memset() is expected to be used with M=0, you cannot do any serious
> optimisations to it at all. If memset() is expected to be used with I=1
> it should use a separate code path for it, probably the caller should
> make the distinction.
DMA coherent memory which uses uncached memory for platforms that
do not provide hardware dma coherence can end up just about anywhere
in the kernel. We could use special routines for a few places in
the DMA subsystem, but there might be plenty of others.
next prev parent reply other threads:[~2024-08-23 13:55 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-16 14:52 [PATCH v2] powerpc: warn on emulation of dcbz instruction in kernel mode Christophe Leroy
2021-11-02 10:11 ` Michael Ellerman
2024-08-21 22:39 ` Christian Lamparter
2024-08-22 5:25 ` LEROY Christophe
2024-08-22 5:32 ` Christoph Hellwig
2024-08-22 6:39 ` LEROY Christophe
2024-08-22 7:14 ` Christoph Hellwig
2024-08-22 9:53 ` Benjamin Herrenschmidt
2024-08-22 18:19 ` Christian Lamparter
2024-08-23 8:07 ` Christoph Hellwig
2024-08-23 13:06 ` Segher Boessenkool
2024-08-23 13:54 ` Christoph Hellwig [this message]
2024-08-23 19:19 ` Segher Boessenkool
2024-08-23 23:43 ` Christian Lamparter
2024-08-24 9:01 ` LEROY Christophe
2024-08-24 17:17 ` Segher Boessenkool
2024-08-27 7:29 ` Christoph Hellwig
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=20240823135459.GA28487@lst.de \
--to=hch@lst.de \
--cc=benh@kernel.crashing.org \
--cc=christian.lamparter@isd.uni-stuttgart.de \
--cc=christophe.leroy2@cs-soprasteria.com \
--cc=fthain@linux-m68k.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mpe@ellerman.id.au \
--cc=paulus@samba.org \
--cc=segher@kernel.crashing.org \
--cc=userm57@yahoo.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).