[PATCH v2 03/22] ARM: use late patch framework for phys-virt patching

On Sun, 12 Aug 2012, Cyril Chemparathy wrote:

On 08/11/12 23:03, Nicolas Pitre wrote:

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On Fri, 10 Aug 2012, Cyril Chemparathy wrote:

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-extern unsigned long __pv_phys_offset;
-#define PHYS_OFFSET __pv_phys_offset

[...]

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+#define PHYS_OFFSET	__virt_to_phys(PAGE_OFFSET)

What was wrong with the former PHYS_OFFSET = __pv_phys_offset ?

If you really want to have it optimized at run time, you could simply
use your new stub to patch a mov instruction instead of going through
__virt_to_phys which uses and add on top of a constant.

The intent was to optimize out the load(s) on references to PHYS_OFFSET, but
is it worth it?  If so, we could go with a patched mov (or two) with the
necessary endian fixups.  If not, we could revert to __pv_phys_offset loads as
before.

If you want to do better than the load, then you'd better go all the way 
with the patched move.

quoted

You also should remove the MODULE_ARCH_VERMAGIC_P2V definitions now that
the corresponding code is no longer there.

Hmm...

"rt-patch" needs to be in vermagic to prevent modules built against the new
code from being loaded on older kernels that used the traditional patch code.

Right.

"p2v" needs to be in there as well, because it should be possible to build
without PATCH_PHYS_VIRT, but with RUNTIME_PATCH as and when there are other
users for this.

That doesn't matter if there are other users.  As soon as there is a 
.init.runtime_patch_table that needs to be processed then "rt-patch" 
flags it.  Whether this is used for PATCH_PHYS_VIRT or other purposes is 
irrelevant.

However there isn't any pv_table anymore, so "p2v" should go as there is 
no more code to process those tables if they're ever encountered.


Nicolas