Re: [patch 134/149] x86, paravirt: Add a global synchronization point for pvclock

Jeremy Fitzhardinge
2010-07-14T20:40:22Z

On 07/14/2010 01:16 PM, Avi Kivity wrote:
> On 07/14/2010 08:57 PM, Jeremy Fitzhardinge wrote:
>> Anything else?
>
> 1. set up a mapping
> 2. invlpg or set cr3
> 3. use the mapping
>
> Moving the invlpg will break your code.

invlpg uses memory clobbers. All the crX ops seem to use a
__force_order variable to sequence them - but it looks like it's done
precisely backwards and it's barking mad to do allow write_crX to be
reordered with respect to memory ops.

Hm, looks like glommer added it surreptitiously while unifying
system_32.h and system_64.h (system_32.h relied on asm volatile not
being reordered; system_64.h used memory clobbers).
J