[Qemu-devel] Re: [PATCH 0/9] S390x KVM support

[Alexander Graf <agraf@suse.de>]

On 22.10.2009, at 11:08, Avi Kivity wrote:

> On 10/20/2009 06:40 PM, Carsten Otte wrote:
>>
>> This patch moves s390 processor status word into the base kvm_run
>> struct and keeps it up-to date on all userspace exits.
>>
>> +#include <linux/autoconf.h>
>> #include <linux/types.h>
>> #include <linux/compiler.h>
>> #include <linux/ioctl.h>
>
> Not needed.
>
>> @@ -116,6 +117,11 @@
>>    __u64 cr8;
>>    __u64 apic_base;
>>
>> +#ifdef CONFIG_S390
>> +    /* the processor status word for s390 */
>> +    __u64 psw_mask; /* psw upper half */
>> +    __u64 psw_addr; /* psw lower half */
>> +#endif
>
> Doesn't this break backward compatibility by changing the structure?
>
> Best to put it after the union (and as a copy, so userspace that  
> expects the previous location still works).  If you're reading it  
> from the kernel, also need a way to tell the kernel which copy to  
> read from.
>
> Also advertise with a KVM_CAP.

I don't think we need to go through the hassle here. There is  
effectively no user of that code for now and the ABI is considered  
unstable.

> Additionally, CONFIG_ in public headers are frowned upon as non- 
> portable.  A workaround is to #define __KVM_S390 in <asm/kvm.h> and  
> depend on that.
>
>> --- kvm.orig/arch/s390/kvm/kvm-s390.c    2009-10-20  
>> 15:01:02.000000000 +0200
>> +++ kvm/arch/s390/kvm/kvm-s390.c    2009-10-20 18:13:45.000000000  
>> +0200
>> @@ -421,7 +421,8 @@
>>    if (atomic_read(&vcpu->arch.sie_block->cpuflags) &  
>> CPUSTAT_RUNNING)
>>        rc = -EBUSY;
>>    else
>> -        vcpu->arch.sie_block->gpsw = psw;
>> +        vcpu->run->psw_mask = psw.mask;
>> +        vcpu->run->psw_addr = psw.addr;
>
> It's traditional to add braces around multi-line else blocks.
>
> I'd also appreciate an explanation of what this is all about.

Explanation in the code or explanation in an email reply?

Alex