Re: handle_mm_fault() calling convention cleanup..

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Sun, 2009-06-21 at 13:42 -0700, Linus Torvalds wrote:
> Just a heads up that I committed the patches that I sent out two months 
> ago to make the fault handling routines use the finer-grained fault flags 
> (FAULT_FLAG_xyzzy) rather than passing in a boolean for "write".
> 
> That was originally for the NOPAGE_RETRY patches, but it's a general 
> cleanup too. I have this suspicion that we should extend this to 
> "get_user_pages()" too, instead of having those boolean "write" and 
> "force" flags (and GUP_FLAGS_xyzzy as opposed to FAULT_FLAGS_yyzzy).

BTW. I'd like to extend these if there's no objection one of these days
to also pass whether it was an exec fault, and pass the full flags to
ptep_set_access_flags().

That would (finally) give us a better hook for architectures that need
to do it to handle i$/d$ coherency. Right now, I go dig for the current
fault type inside the current pt_regs from ptep_set_access_flags() which
is positively ugly.

Ben.

> We should probably also get rid of the insane FOLL_xyz flags too. Right 
> now the code in fact depends on FOLL_WRITE being the same as 
> FAULT_FLAGS_WRITE, and while that is a simple dependency, it's just crazy 
> how we have all these different flags for what ends up often boiling down 
> to the same fundamental issue in the end (even if not all versions of the 
> flags are necessarily always valid for all uses).
> 
> I fixed up all architectures that I noticed (at least microblaze had been 
> added since the original patches in April), but arch maintainers should 
> double-check. Arch maintainers might also want to check whether the 
> mindless conversion of
> 
> 	'is_write' => 'is_write ? FAULT_FLAGS_WRITE : 0'
> 
> might perhaps be written in some more natural way (for example, maybe 
> you'd like to get rid of 'iswrite' as a variable entirely, and replace it 
> with a 'fault_flags' variable).
> 
> It's pushed out and tested on x86-64, but it really was such a mindless 
> conversion that I hope it works on all architectures. But I thought I'd 
> better give people a shout-out regardless.
> 
> 		Linus
> 
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