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

[Andi Kleen <andi@firstfloor.org>]

> 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.

-Andi