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

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

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

quoted

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