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

Alexander Graf
2010-06-27T09:40:21Z

Am 27.06.2010 um 10:21 schrieb Avi Kivity <avi-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>:

> 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.

>
> Why won't zero/nonzero work for this?

Because there is no store immediate opcode on powerpc :(.

Alex