On 04/12/2010 05:29 AM, Takuya Yoshikawa wrote:
TODO:
1. We want to use copy_in_user() for 32bit case too.
Definitely. Why doesn't it work now?
Sadly we don't have that for 32bit. We have to implement by ourselves.
I tested two temporary implementations for 32bit:
1. This version using copy_from_user() and copy_to_user() with
not nice vmalloc().
2. Loop with __get_user() and __put_user().
The result was 1 is much faster than 2.
What about copy_from_user()/copy_to_user() through a 512 byte buffer on
the kernel stack? That should give the speed of 1 without the vmalloc()
(which will fail on 32 bit if you copy large blocks).
Note that this is only for the compatibility issue: in the future,
we hope, qemu will not need to use this ioctl.
2. We have to implement test_bit_user() to avoid extra set_bit.
This was important in the days of shadow paging. I'm not so sure about
it with nested paging, since we'll typically only fault a page once per
iteration. Since we're very likely to actually write these days, the
extra access is wasteful.
Nice news for me! So all we need to ask x86(asm-generic) people to
merge are:
set bit user and copy_in_user 32bit version.
They might still want test_bit_user and clear_bit_user for completeness :)
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
