diff options
Diffstat (limited to 'Documentation/core-api')
| -rw-r--r-- | Documentation/core-api/cachetlb.rst | 86 |
1 files changed, 37 insertions, 49 deletions
diff --git a/Documentation/core-api/cachetlb.rst b/Documentation/core-api/cachetlb.rst index fe4290e26729..8aed9103e48a 100644 --- a/Documentation/core-api/cachetlb.rst +++ b/Documentation/core-api/cachetlb.rst @@ -271,10 +271,15 @@ maps this page at its virtual address. ``void flush_dcache_page(struct page *page)`` - Any time the kernel writes to a page cache page, _OR_ - the kernel is about to read from a page cache page and - user space shared/writable mappings of this page potentially - exist, this routine is called. + This routines must be called when: + + a) the kernel did write to a page that is in the page cache page + and / or in high memory + b) the kernel is about to read from a page cache page and user space + shared/writable mappings of this page potentially exist. Note + that {get,pin}_user_pages{_fast} already call flush_dcache_page + on any page found in the user address space and thus driver + code rarely needs to take this into account. .. note:: @@ -284,38 +289,34 @@ maps this page at its virtual address. handling vfs symlinks in the page cache need not call this interface at all. - The phrase "kernel writes to a page cache page" means, - specifically, that the kernel executes store instructions - that dirty data in that page at the page->virtual mapping - of that page. It is important to flush here to handle - D-cache aliasing, to make sure these kernel stores are - visible to user space mappings of that page. - - The corollary case is just as important, if there are users - which have shared+writable mappings of this file, we must make - sure that kernel reads of these pages will see the most recent - stores done by the user. - - If D-cache aliasing is not an issue, this routine may - simply be defined as a nop on that architecture. - - There is a bit set aside in page->flags (PG_arch_1) as - "architecture private". The kernel guarantees that, - for pagecache pages, it will clear this bit when such - a page first enters the pagecache. - - This allows these interfaces to be implemented much more - efficiently. It allows one to "defer" (perhaps indefinitely) - the actual flush if there are currently no user processes - mapping this page. See sparc64's flush_dcache_page and - update_mmu_cache implementations for an example of how to go - about doing this. - - The idea is, first at flush_dcache_page() time, if - page->mapping->i_mmap is an empty tree, just mark the architecture - private page flag bit. Later, in update_mmu_cache(), a check is - made of this flag bit, and if set the flush is done and the flag - bit is cleared. + The phrase "kernel writes to a page cache page" means, specifically, + that the kernel executes store instructions that dirty data in that + page at the page->virtual mapping of that page. It is important to + flush here to handle D-cache aliasing, to make sure these kernel stores + are visible to user space mappings of that page. + + The corollary case is just as important, if there are users which have + shared+writable mappings of this file, we must make sure that kernel + reads of these pages will see the most recent stores done by the user. + + If D-cache aliasing is not an issue, this routine may simply be defined + as a nop on that architecture. + + There is a bit set aside in page->flags (PG_arch_1) as "architecture + private". The kernel guarantees that, for pagecache pages, it will + clear this bit when such a page first enters the pagecache. + + This allows these interfaces to be implemented much more efficiently. + It allows one to "defer" (perhaps indefinitely) the actual flush if + there are currently no user processes mapping this page. See sparc64's + flush_dcache_page and update_mmu_cache implementations for an example + of how to go about doing this. + + The idea is, first at flush_dcache_page() time, if page_file_mapping() + returns a mapping, and mapping_mapped on that mapping returns %false, + just mark the architecture private page flag bit. Later, in + update_mmu_cache(), a check is made of this flag bit, and if set the + flush is done and the flag bit is cleared. .. important:: @@ -351,19 +352,6 @@ maps this page at its virtual address. architectures). For incoherent architectures, it should flush the cache of the page at vmaddr. - ``void flush_kernel_dcache_page(struct page *page)`` - - When the kernel needs to modify a user page is has obtained - with kmap, it calls this function after all modifications are - complete (but before kunmapping it) to bring the underlying - page up to date. It is assumed here that the user has no - incoherent cached copies (i.e. the original page was obtained - from a mechanism like get_user_pages()). The default - implementation is a nop and should remain so on all coherent - architectures. On incoherent architectures, this should flush - the kernel cache for page (using page_address(page)). - - ``void flush_icache_range(unsigned long start, unsigned long end)`` When the kernel stores into addresses that it will execute |