[PATCH 08/26] KVM: PPC: Add PV guest critical sections

[Avi Kivity]

On 06/27/2010 12:40 PM, Alexander Graf wrote:
>
> Am 27.06.2010 um 10:21 schrieb Avi Kivity <avi at redhat.com>:
>
>> On 06/26/2010 02:24 AM, Alexander Graf wrote:
>>> When running in hooked code we need a way to disable interrupts without
>>> clobbering any interrupts or exiting out to the hypervisor.
>>>
>>> To achieve this, we have an additional critical field in the shared 
>>> page. If
>>> that field is equal to the r1 register of the guest, it tells the 
>>> hypervisor
>>> that we're in such a critical section and thus may not receive any 
>>> interrupts.
>>>
>>
>> Is r1 reserved for this purpose?  Can't it match accidentally?
>
> r1 is defined by the abi to be the stack.

Neat trick!

>>
>> Why won't zero/nonzero work for this?
>
> Because there is no store immediate opcode on powerpc :(.

Or inc/dec...

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