Re: [Xen-devel] [PATCH] "lock cmpxch8b" and split locks

Keir Fraser
Wed, 05 Oct 2005 22:02:31 -0000

On 5 Oct 2005, at 22:46, Keir Fraser wrote:

>> Does anyone know if there are other places where the "lock"
prefix is
>> used with a cache misaligned address?
>
> x86 systems are supposed to guarantee that LOCKed instructions access
> their memory operand atomically, regardless of alignment (Vol 3 of the
> Intel reference manual). Your systems break this application-visible
> guarantee?

Also, the patch is way bigger and more invasive than it needs to be.
There should be no need to make pfn_info bigger than it is. It''s
currently a multiple of 8 bytes (e.g., 24 bytes on 32-bit) which is
sufficient to avoid cache-line crossing of aligned 8-byte quantities.

What if we just move ''tlbflush_timestamp'' to the end of the
structure?
A one-line fix? :-)

  -- Keir