Re: [RFC PATCH 3/3] KVM: MMU: Optimize guest page table walk

[Avi Kivity <avi@redhat.com>]

On 04/29/2011 07:05 PM, Andi Kleen wrote:
> >  Do you think the following case would not differ so much
> >  from (1' 2') ?
> >
> >  walk_addr_generic()              ---1''
> >    copy_from_user()               ---2''
>
> Yes it should be the same and is cleaner.
>
> If you do a make .../foo.i and look at the code coming out of the
> preprocessor you'll see it expands to a
>
> 	if (!__builtin_constant_p(size))
>                  return copy_user_generic(dst, (__force void *)src, size);
>          switch (size) {
>          case 1:__get_user_asm(*(u8 *)dst, (u8 __user *)src,
>                                ret, "b", "b", "=q", 1);
>                  return ret;
> 	case 2: ..
> 	case 4: ..
> 	case 8: ..
> 	case 10: ..
> 	case 16: ..
> 	}
>
> Ok it looks like the 32bit kernel only handles 1/2/4. Maybe that
> was the problem if you ran on 32bit.

I'm happy with a slower copy_from_user() for that particular case.

-- 
error compiling committee.c: too many arguments to function