Re: [Qemu-devel] [PATCH] spapr: reset @kvm_vcpu_dirty before starting CPU

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 01/21/2014 01:45 AM, Alexander Graf wrote:
> 
> On 15.01.2014, at 05:57, Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
> 
>> Normally QEMU kvm_arch_get_registers() reads registers and sets a dirty
>> flag which prevents further registers reading from KVM till
>> kvm_arch_put_registers() executes and resets the flag.
>>
>> However if we run QEMU with "-S" ("suspended"), then execute "info cpus"
>> from the QEMU monitor, we end up with not reading registers in
>> rtas_start_cpu() as qmp_query_cpus() calls kvm_cpu_synchronize_state()
>> which leaves @kvm_vcpu_dirty=true what prevents kvm_cpu_synchronize_state()
>> from synchronizing registers and we loose the values.
> 

> But that's fine because the values are already synchronized and couldn't
> have changed because the guest cpu wasn't running, no?


Discovered today that "[PATCH] spapr: fix H_SET_MODE to sync LPCR with KVM"
seems to be v2 of this as that patch solves the issue this patch was
intended to solve so I'll drop this one.




> 
> 
> Alex
> 
>>
>> This resets @kvm_vcpu_dirty flag as we do not have content which we really want to
>> keep at this point as the CPU is halted.
>>
>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>> ---
>>
>> We could also reset @kvm_vcpu_dirty in qmp_query_cpus() but that would be
>> racy.
>> ---
>> hw/ppc/spapr_rtas.c | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
>> index 1cb276d..3dade5e 100644
>> --- a/hw/ppc/spapr_rtas.c
>> +++ b/hw/ppc/spapr_rtas.c
>> @@ -185,6 +185,8 @@ static void rtas_start_cpu(PowerPCCPU *cpu_, sPAPREnvironment *spapr,
>>         /* This will make sure qemu state is up to date with kvm, and
>>          * mark it dirty so our changes get flushed back before the
>>          * new cpu enters */
>> +
>> +        cs->kvm_vcpu_dirty = false;
>>         kvm_cpu_synchronize_state(cs);
>>
>>         env->msr = (1ULL << MSR_SF) | (1ULL << MSR_ME);
>> -- 
>> 1.8.4.rc4
>>
> 


-- 
Alexey