From: deller@kernel.org
To: linux-parisc@vger.kernel.org
Cc: Helge Deller <deller@gmx.de>
Subject: [PATCH] parisc: shmparam.h: Document aliasing requirements of PA-RISC
Date: Fri, 1 Sep 2023 08:04:31 +0200 [thread overview]
Message-ID: <20230901060431.6170-1-deller@kernel.org> (raw)
From: Helge Deller <deller@gmx.de>
Add some documentation why PA-RISC uses SHMLBA and SHM_COLOUR.
Signed-off-by: Helge Deller <deller@gmx.de>
---
arch/parisc/include/asm/shmparam.h | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/arch/parisc/include/asm/shmparam.h b/arch/parisc/include/asm/shmparam.h
index 74f74e4d35b7..5a95b0f62b87 100644
--- a/arch/parisc/include/asm/shmparam.h
+++ b/arch/parisc/include/asm/shmparam.h
@@ -2,6 +2,21 @@
#ifndef _ASMPARISC_SHMPARAM_H
#define _ASMPARISC_SHMPARAM_H
+/*
+ * PA-RISC uses virtually indexed & physically tagged (VIPT) caches
+ * which has strict requirements when two pages to the same physical
+ * address are accessed through different mappings. Read the section
+ * "Address Aliasing" in the arch docs for more detail:
+ * PA-RISC 1.1 (page 3-6):
+ * https://parisc.wiki.kernel.org/images-parisc/6/68/Pa11_acd.pdf
+ * PA-RISC 2.0 (page F-5):
+ * https://parisc.wiki.kernel.org/images-parisc/7/73/Parisc2.0.pdf
+ *
+ * For Linux we allow kernel and userspace to map pages on page size
+ * granularity (SHMLBA) but have to ensure that, if two pages are
+ * mapped to the same physical address, the virtual and physical
+ * addresses modulo SHM_COLOUR are identical.
+ */
#define SHMLBA PAGE_SIZE /* attach addr a multiple of this */
#define SHM_COLOUR 0x00400000 /* shared mappings colouring */
--
2.41.0
next reply other threads:[~2023-09-01 6:04 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-01 6:04 deller [this message]
2023-09-04 17:57 ` [PATCH] parisc: shmparam.h: Document aliasing requirements of PA-RISC John David Anglin
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=20230901060431.6170-1-deller@kernel.org \
--to=deller@kernel.org \
--cc=deller@gmx.de \
--cc=linux-parisc@vger.kernel.org \
/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 read-only IMAP folder(s) and NNTP newsgroup(s).