Re: [Qemu-devel] [Qemu-ppc] [PATCH 5/5] target-ppc: Handle cases when multi-processors get machine-check

[Aravinda Prasad <aravinda@linux.vnet.ibm.com>]

On Wednesday 27 August 2014 04:10 PM, Alexander Graf wrote:
> 
> 
> On 25.08.14 15:45, Aravinda Prasad wrote:
>> It is possible for multi-processors to experience machine
>> check at or about the same time. As per PAPR, subsequent
>> processors serialize waiting for the first processor to
>> issue the ibm,nmi-interlock call.
>>
>> The second processor retries if the first processor which
>> received a machine check is still reading the error log
>> and is yet to issue ibm,nmi-interlock call.
>>
>> This patch implements this functionality.
>>
>> Signed-off-by: Aravinda Prasad <aravinda@linux.vnet.ibm.com>
> 
> This patch doesn't make any sense. Both threads will issue an HCALL
> which will get locked inside of QEMU, so we'll never see the case where
> both hypercalls get processed at the same time.

AFAIK, only one thread can succeed entering qemu upon parallel hcall
from different guest CPUs as it is gated by a lock. Hence one hcall is
processed at a time.

As per PAPR, we don't want any other KVMPPC_H_REPORT_ERR hcall to be
processed at the same time and further KVMPPC_H_REPORT_ERR hcall thus
issued should wait until the OS issues ibm,nmi-interlock.

Thanks for the review.

Regards,
Aravinda

> 
> 
> Alex
> 

-- 
Regards,
Aravinda