Re: [Qemu-devel] ppc64 not resuming with v2.3.0-rc3

[Stefan Berger <stefanb@linux.vnet.ibm.com>]

On 04/16/2015 03:42 PM, Mark Cave-Ayland wrote:
> On 16/04/15 17:43, Stefan Berger wrote:
>
>> The culprit patch seems to be the following commit. If I remove these
>> changes from the tip of the tree it works again (on SLOF level):
>>
>> commit 2360b6e84f78d41fa0f76555a947148b73645259
>> Author: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
>> Date:   Mon Feb 9 22:40:48 2015 +0000
>>
>>      target-ppc: force update of msr bits in cpu_post_load
>>
>>      Since env->msr has already been restored by the time cpu_post_load
>> is called,
>>      make sure that ppc_store_msr() is explicitly called with all msr
>> bits except
>>      MSR_TGPR marked as invalid.
>>
>>      This solves the issue where MSR flags aren't set correctly when
>> restoring a VM
>>      snapshot, in particular the internal env->excp_prefix value when
>> MSR_EP has
>>      been altered by a guest.
>>
>>      Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
>>      Signed-off-by: Alexander Graf <agraf@suse.de>
>>
>> diff --git a/target-ppc/machine.c b/target-ppc/machine.c
>> index c801b82..3921012 100644
>> --- a/target-ppc/machine.c
>> +++ b/target-ppc/machine.c
>> @@ -159,6 +159,7 @@ static int cpu_post_load(void *opaque, int version_id)
>>       PowerPCCPU *cpu = opaque;
>>       CPUPPCState *env = &cpu->env;
>>       int i;
>> +    target_ulong msr;
>>
>>       /*
>>        * We always ignore the source PVR. The user or management
>> @@ -190,7 +191,12 @@ static int cpu_post_load(void *opaque, int version_id)
>>           /* Restore htab_base and htab_mask variables */
>>           ppc_store_sdr1(env, env->spr[SPR_SDR1]);
>>       }
>> -    hreg_compute_hflags(env);
>> +
>> +    /* Mark msr bits except MSR_TGPR invalid before restoring */
>> +    msr = env->msr;
>> +    env->msr ^= ~(1ULL << MSR_TGPR);
>> +    ppc_store_msr(env, msr);
>> +
>>       hreg_compute_mem_idx(env);
>>
>>       return 0;
>>
>>
>>     Stefan
>>
>> PS: Sorry for the late notice (-rc3), but I only started doing things
>> with ppc64 a few days ago.
> Hmmmm the fix is correct in that internal MSR variables need to be
> updated post-restore (as noted in the message above it was the exception
> prefix variables that weren't updated by having MSR_EP set).
>
> Maybe on ppc64 there is another bit similar to MSR_TGPR that needs to be
> excluded? Alex, any thoughts?

I want to add that I am running QEMU for ppc64 in emulation mode on a 
x86_64 host. The suspend/resume problem, while in SLOF, did not exist in 
QEMU v2.2, so I anticipate that this is a regression would also be 
visible on QEMU on kvm, though a simple test on such a machine may show 
different...

Removing the patch solves the problem while in SLOF. Once booting into 
Linux suspend/resume does not work - with qemu-system-ppc64 on x86_64 
host. Timestamps shown by Linux actually make a jump backwards and 
ultimately Linux hangs.


      Stefan


>
> ATB,
>
> Mark.
>
>