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From: Alexander Graf <agraf@suse.de>
To: Avi Kivity <avi@redhat.com>
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Subject: Re: [PATCH 08/26] KVM: PPC: Add PV guest critical sections
Date: Sun, 27 Jun 2010 11:40:21 +0200
Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
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Am 27.06.2010 um 10:21 schrieb Avi Kivity <avi@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.

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

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

Alex