- Cache and TLB Flushing
- Under Linux
+==================================
+Cache and TLB Flushing Under Linux
+==================================
- David S. Miller <davem@redhat.com>
+:Author: David S. Miller <davem@redhat.com>
This document describes the cache/tlb flushing interfaces called
by the Linux VM subsystem. It enumerates over each interface,
invoke one of the following flush methods _after_ the page table
changes occur:
-1) void flush_tlb_all(void)
+1) ``void flush_tlb_all(void)``
The most severe flush of all. After this interface runs,
any previous page table modification whatsoever will be
This is usually invoked when the kernel page tables are
changed, since such translations are "global" in nature.
-2) void flush_tlb_mm(struct mm_struct *mm)
+2) ``void flush_tlb_mm(struct mm_struct *mm)``
This interface flushes an entire user address space from
the TLB. After running, this interface must make sure that
page table operations such as what happens during
fork, and exec.
-3) void flush_tlb_range(struct vm_area_struct *vma,
- unsigned long start, unsigned long end)
+3) ``void flush_tlb_range(struct vm_area_struct *vma,
+ unsigned long start, unsigned long end)``
Here we are flushing a specific range of (user) virtual
address translations from the TLB. After running, this
call flush_tlb_page (see below) for each entry which may be
modified.
-4) void flush_tlb_page(struct vm_area_struct *vma, unsigned long addr)
+4) ``void flush_tlb_page(struct vm_area_struct *vma, unsigned long addr)``
This time we need to remove the PAGE_SIZE sized translation
from the TLB. The 'vma' is the backing structure used by
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(struct vm_area_struct *vma,
+ unsigned long address, pte_t *ptep)``
At the end of every page fault, this routine is invoked to
tell the architecture specific code that a translation
translations for software managed TLB configurations.
The sparc64 port currently does this.
-6) void tlb_migrate_finish(struct mm_struct *mm)
+6) ``void tlb_migrate_finish(struct mm_struct *mm)``
This interface is called at the end of an explicit
process migration. This interface provides a hook
Next, we have the cache flushing interfaces. In general, when Linux
is changing an existing virtual-->physical mapping to a new value,
-the sequence will be in one of the following forms:
+the sequence will be in one of the following forms::
1) flush_cache_mm(mm);
change_all_page_tables_of(mm);
Here are the routines, one by one:
-1) void flush_cache_mm(struct mm_struct *mm)
+1) ``void flush_cache_mm(struct mm_struct *mm)``
This interface flushes an entire user address space from
the caches. That is, after running, there will be no cache
This interface is used to handle whole address space
page table operations such as what happens during exit and exec.
-2) void flush_cache_dup_mm(struct mm_struct *mm)
+2) ``void flush_cache_dup_mm(struct mm_struct *mm)``
This interface flushes an entire user address space from
the caches. That is, after running, there will be no cache
This option is separate from flush_cache_mm to allow some
optimizations for VIPT caches.
-3) void flush_cache_range(struct vm_area_struct *vma,
- unsigned long start, unsigned long end)
+3) ``void flush_cache_range(struct vm_area_struct *vma,
+ unsigned long start, unsigned long end)``
Here we are flushing a specific range of (user) virtual
addresses from the cache. After running, there will be no
call flush_cache_page (see below) for each entry which may be
modified.
-4) void flush_cache_page(struct vm_area_struct *vma, unsigned long addr, unsigned long pfn)
+4) ``void flush_cache_page(struct vm_area_struct *vma, unsigned long addr, unsigned long pfn)``
This time we need to remove a PAGE_SIZE sized range
from the cache. The 'vma' is the backing structure used by
This is used primarily during fault processing.
-5) void flush_cache_kmaps(void)
+5) ``void flush_cache_kmaps(void)``
This routine need only be implemented if the platform utilizes
highmem. It will be called right before all of the kmaps
This routing should be implemented in asm/highmem.h
-6) void flush_cache_vmap(unsigned long start, unsigned long end)
- void flush_cache_vunmap(unsigned long start, unsigned long end)
+6) ``void flush_cache_vmap(unsigned long start, unsigned long end)``
+ ``void flush_cache_vunmap(unsigned long start, unsigned long end)``
Here in these two interfaces we are flushing a specific range
of (kernel) virtual addresses from the cache. After running,
processes to mmap shared memory at address which are a multiple of
this value.
-NOTE: This does not fix shared mmaps, check out the sparc64 port for
-one way to solve this (in particular SPARC_FLAG_MMAPSHARED).
+.. note::
+
+ This does not fix shared mmaps, check out the sparc64 port for
+ one way to solve this (in particular SPARC_FLAG_MMAPSHARED).
Next, you have to solve the D-cache aliasing issue for all
other cases. Please keep in mind that fact that, for a given page
aliasing problem has the potential to exist since the kernel already
maps this page at its virtual address.
- void copy_user_page(void *to, void *from, unsigned long addr, struct page *page)
- void clear_user_page(void *to, unsigned long addr, struct page *page)
+ ``void copy_user_page(void *to, void *from, unsigned long addr, struct page *page)``
+ ``void clear_user_page(void *to, unsigned long addr, struct page *page)``
These two routines store data in user anonymous or COW
pages. It allows a port to efficiently avoid D-cache alias
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_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.
- NOTE: This routine need only be called for page cache pages
+ .. note::
+
+ This routine need only be called for page cache pages
which can potentially ever be mapped into the address
space of a user process. So for example, VFS layer code
handling vfs symlinks in the page cache need not call
made of this flag bit, and if set the flush is done and the flag
bit is cleared.
- IMPORTANT NOTE: It is often important, if you defer the flush,
+ .. important::
+
+ It is often important, if you defer the flush,
that the actual flush occurs on the same CPU
as did the cpu stores into the page to make it
dirty. Again, see sparc64 for examples of how
to deal with this.
- void copy_to_user_page(struct vm_area_struct *vma, struct page *page,
- unsigned long user_vaddr,
- void *dst, void *src, int len)
- void copy_from_user_page(struct vm_area_struct *vma, struct page *page,
- unsigned long user_vaddr,
- void *dst, void *src, int len)
+ ``void copy_to_user_page(struct vm_area_struct *vma, struct page *page,
+ unsigned long user_vaddr, void *dst, void *src, int len)``
+ ``void copy_from_user_page(struct vm_area_struct *vma, struct page *page,
+ unsigned long user_vaddr, void *dst, void *src, int len)``
+
When the kernel needs to copy arbitrary data in and out
of arbitrary user pages (f.e. for ptrace()) it will use
these two routines.
likely that you will need to flush the instruction cache
for copy_to_user_page().
- void flush_anon_page(struct vm_area_struct *vma, struct page *page,
- unsigned long vmaddr)
+ ``void flush_anon_page(struct vm_area_struct *vma, struct page *page,
+ unsigned long vmaddr)``
+
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
architectures). For incoherent architectures, it should flush
the cache of the page at vmaddr.
- void flush_kernel_dcache_page(struct page *page)
+ ``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
the kernel cache for page (using page_address(page)).
- void flush_icache_range(unsigned long start, unsigned long end)
+ ``void flush_icache_range(unsigned long start, unsigned long end)``
+
When the kernel stores into addresses that it will execute
out of (eg when loading modules), this function is called.
If the icache does not snoop stores then this routine will need
to flush it.
- void flush_icache_page(struct vm_area_struct *vma, struct page *page)
+ ``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
is to remove this interface completely.
coherency. It must do this by flushing the vmap range before doing
I/O and invalidating it after the I/O returns.
- void flush_kernel_vmap_range(void *vaddr, int size)
+ ``void flush_kernel_vmap_range(void *vaddr, int size)``
+
flushes the kernel cache for a given virtual address range in
the vmap area. This is to make sure that any data the kernel
modified in the vmap range is made visible to the physical
Note that this API does *not* also flush the offset map alias
of the area.
- void invalidate_kernel_vmap_range(void *vaddr, int size) invalidates
+ ``void invalidate_kernel_vmap_range(void *vaddr, int size) invalidates``
+
the cache for a given virtual address range in the vmap area
which prevents the processor from making the cache stale by
speculatively reading data while the I/O was occurring to the
projects / platform / kernel / linux-exynos.git / commitdiff