Re: [Qemu-devel] [PATCH v4] s390: diagnose 318 info reset and migration support

[David Hildenbrand]

On 14.05.19 11:00, Cornelia Huck wrote:
> On Tue, 14 May 2019 10:56:43 +0200
> Christian Borntraeger <address@hidden> wrote:
> 
>> On 14.05.19 10:50, David Hildenbrand wrote:
> 
>>> Another idea for temporary handling: Simply only indicate 240 CPUs to
>>> the guest if the response does not fit into a page. Once we have that
>>> SCLP thingy, this will be fixed. Guest migration back and forth should
>>> work, as the VCPUs are fully functional (and initially always stopped),
>>> the guest will simply not be able to detect them via SCLP when booting
>>> up, and therefore not use them.  
>>
>> Yes, that looks like a good temporary solution. In fact if the guest relies
>> on simply probing it could even make use of the additional CPUs. Its just
>> the sclp response that is limited to 240 (or make it 247?)
> 
> Where did the 240 come from - extra spare room? If so, 247 would
> probably be all right?
> 

+++ b/include/hw/s390x/sclp.h
@@ -133,6 +133,8 @@ typedef struct ReadInfo {
     uint16_t highest_cpu;
     uint8_t  _reserved5[124 - 122];     /* 122-123 */
     uint32_t hmfai;
+    uint8_t  _reserved7[134 - 128];     /* 128-133 */
+    uint8_t  fac134;
     struct CPUEntry entries[0];
 } QEMU_PACKED ReadInfo;


So we have "4096 - 135 + 1" memory. Each element is 16 bytes wide.
-> 246 CPUs fit.


-- 

Thanks,

David / dhildenb