Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 9df5f741 authored by James Bottomley's avatar James Bottomley
Browse files

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: default avatarJames Bottomley <James.Bottomley@suse.de>
parent 6b7b2849

Documentation/cachetlb.txt

+24 −0
Original line number Original line Diff line number Diff line
@@ -377,3 +377,27 @@ maps this page at its virtual address. 
	All the functionality of flush_icache_page can be implemented in

	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

	flush_dcache_page and update_mmu_cache. In 2.7 the hope is to

	remove this interface completely.

	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.

include/linux/highmem.h

+6 −0
Original line number Original line Diff line number Diff line
@@ -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_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

#endif





#include <asm/kmap_types.h>

#include <asm/kmap_types.h>