diff options
Diffstat (limited to 'Documentation/core-api/cachetlb.rst')
| -rw-r--r-- | Documentation/core-api/cachetlb.rst | 103 |
1 files changed, 48 insertions, 55 deletions
diff --git a/Documentation/core-api/cachetlb.rst b/Documentation/core-api/cachetlb.rst index 93cb65d52720..889fc84ccd1b 100644 --- a/Documentation/core-api/cachetlb.rst +++ b/Documentation/core-api/cachetlb.rst @@ -88,13 +88,17 @@ changes occur: This is used primarily during fault processing. -5) ``void update_mmu_cache(struct vm_area_struct *vma, - unsigned long address, pte_t *ptep)`` +5) ``void update_mmu_cache_range(struct vm_fault *vmf, + struct vm_area_struct *vma, unsigned long address, pte_t *ptep, + unsigned int nr)`` - At the end of every page fault, this routine is invoked to - tell the architecture specific code that a translation - now exists at virtual address "address" for address space - "vma->vm_mm", in the software page tables. + At the end of every page fault, this routine is invoked to tell + the architecture specific code that translations now exists + in the software page tables for address space "vma->vm_mm" + at virtual address "address" for "nr" consecutive pages. + + This routine is also invoked in various other places which pass + a NULL "vmf". A port may use this information in any way it so chooses. For example, it could use this event to pre-load TLB @@ -213,9 +217,9 @@ Here are the routines, one by one: there will be no entries in the cache for the kernel address space for virtual addresses in the range 'start' to 'end-1'. - The first of these two routines is invoked after map_vm_area() + The first of these two routines is invoked after vmap_range() has installed the page table entries. The second is invoked - before unmap_kernel_range() deletes the page table entries. + before vunmap_range() deletes the page table entries. There exists another whole class of cpu cache issues which currently require a whole different set of interfaces to handle properly. @@ -269,12 +273,17 @@ maps this page at its virtual address. If D-cache aliasing is not an issue, these two routines may simply call memcpy/memset directly and do nothing more. - ``void flush_dcache_page(struct page *page)`` + ``void flush_dcache_folio(struct folio *folio)`` + + This routines must be called when: - 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. + 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_folio + on any page found in the user address space and thus driver + code rarely needs to take this into account. .. note:: @@ -284,38 +293,35 @@ 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 phrase "kernel writes to a page cache page" means, specifically, + that the kernel executes store instructions that dirty data in that + page at the kernel 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. + 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. + 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. + There is a bit set aside in folio->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. + 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_folio and update_mmu_cache_range + implementations for an example of how to go about doing this. + + The idea is, first at flush_dcache_folio() time, if + folio_flush_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_range(), a check is made + of this flag bit, and if set the flush is done and the flag bit + is cleared. .. important:: @@ -345,25 +351,12 @@ maps this page at its virtual address. When the kernel needs to access the contents of an anonymous page, it calls this function (currently only - get_user_pages()). Note: flush_dcache_page() deliberately + get_user_pages()). Note: flush_dcache_folio() deliberately doesn't work for an anonymous page. The default implementation is a nop (and should remain so for all coherent 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 @@ -375,7 +368,7 @@ maps this page at its virtual address. ``void flush_icache_page(struct vm_area_struct *vma, struct page *page)`` All the functionality of flush_icache_page can be implemented in - flush_dcache_page and update_mmu_cache. In the future, the hope + flush_dcache_folio and update_mmu_cache_range. In the future, the hope is to remove this interface completely. The final category of APIs is for I/O to deliberately aliased address |