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mm: add coherence API for DMA to vmalloc/vmap areas 

On Virtually Indexed architectures (which don't do automatic alias
resolution in their caches), we have to flush via the correct
virtual address to prepare pages for DMA.  On some architectures
(like arm) we cannot prevent the CPU from doing data movein along
the alias (and thus giving stale read data), so we not only have to
introduce a flush API to push dirty cache lines out, but also an invalidate
API to kill inconsistent cache lines that may have moved in before
DMA changed the data

Signed-off-by: James Bottomley <James.Bottomley@suse.de>
This commit is contained in:
James Bottomley 2010-01-25 11:42:20 -06:00
parent 6b7b284958
commit 9df5f74194
2 changed files with 30 additions and 0 deletions
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24
Documentation/cachetlb.txt
View File

@ -377,3 +377,27 @@ maps this page at its virtual address.
All the functionality of flush_icache_page can be implemented in
flush_dcache_page and update_mmu_cache. In 2.7 the hope is to
remove this interface completely.
The final category of APIs is for I/O to deliberately aliased address
ranges inside the kernel. Such aliases are set up by use of the
vmap/vmalloc API. Since kernel I/O goes via physical pages, the I/O
subsystem assumes that the user mapping and kernel offset mapping are
the only aliases. This isn't true for vmap aliases, so anything in
the kernel trying to do I/O to vmap areas must manually manage
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)
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
page. The design is to make this area safe to perform I/O on.
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
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
physical pages. This is only necessary for data reads into the
vmap area.

6
include/linux/highmem.h
View File

@ -17,6 +17,12 @@ static inline void flush_anon_page(struct vm_area_struct *vma, struct page *page
static inline void flush_kernel_dcache_page(struct page *page)
{
}
static inline void flush_kernel_vmap_range(void *vaddr, int size)
{
}
static inline void invalidate_kernel_vmap_range(void *vaddr, int size)
{
}
#endif
#include <asm/kmap_types.h>