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| author | Helge Deller <deller@gmx.de> | 2023-09-01 08:04:31 +0200 |
|---|---|---|
| committer | Helge Deller <deller@gmx.de> | 2023-09-07 08:00:32 +0200 |
| commit | 3f091387a39795812aab4303949bbc9baa22c077 (patch) | |
| tree | 698cc18fd6ece70318b1a8b7d628a76695f3b323 /arch/parisc | |
| parent | b1bef1388c427cdad7331a9c8eb4ebbbe5b954b0 (diff) | |
| download | linux-3f091387a39795812aab4303949bbc9baa22c077.tar.gz | |
parisc: shmparam.h: Document aliasing requirements of PA-RISC
Add some documentation why PA-RISC uses SHMLBA and SHM_COLOUR.
Signed-off-by: Helge Deller <deller@gmx.de>
Diffstat (limited to 'arch/parisc')
| -rw-r--r-- | arch/parisc/include/asm/shmparam.h | 15 |
1 files changed, 15 insertions, 0 deletions
diff --git a/arch/parisc/include/asm/shmparam.h b/arch/parisc/include/asm/shmparam.h index 74f74e4d35b72..5a95b0f62b87e 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 */ |