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

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Am 27.06.2010 um 10:21 schrieb Avi Kivity <avi@xxxxxxxxxx>:

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

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