Am 27.06.2010 um 11:52 schrieb Avi Kivity [off-list ref]:

On 06/27/2010 12:40 PM, Alexander Graf wrote:

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Am 27.06.2010 um 10:21 schrieb Avi Kivity [off-list ref]:

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On 06/26/2010 02:24 AM, Alexander Graf wrote:

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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!

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Why won't zero/nonzero work for this?

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

Or inc/dec...

Uh - huh? How would that help?

Alex