Re: [qemu-s390x] [PATCH 1/1] s390x/sclp: fix maxram calculation

[David Hildenbrand]

On 30.07.2018 16:09, Christian Borntraeger wrote:
> We clamp down ram_size to match the sclp increment size. We do
> not do the same for maxram_size, which means for large guests
> with some sizes (e.g. -m 50000) maxram_size differs from ram_size.
> This can break other code (e.g. CMMA migration) which uses maxram_size
> to calculate the number of pages and then throws some errors.
> 
> Fixes: 82fab5c5b90e468f3e9d54c ("s390x/sclp: remove memory hotplug support")
> Signed-off-by: Christian Borntraeger <address@hidden>
> CC: address@hidden
> CC: David Hildenbrand <address@hidden>
> ---
>  hw/s390x/sclp.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
> index bd2a024..4510a80 100644
> --- a/hw/s390x/sclp.c
> +++ b/hw/s390x/sclp.c
> @@ -320,6 +320,7 @@ static void sclp_memory_init(SCLPDevice *sclp)
>      initial_mem = initial_mem >> increment_size << increment_size;
>  
>      machine->ram_size = initial_mem;
> +    machine->maxram_size = initial_mem;
>      /* let's propagate the changed ram size into the global variable. */
>      ram_size = initial_mem;
>  }
> 

BTW, I handle it in may private patch like this

 static inline SCLPDevice *get_sclp_device(void)
 {
@@ -319,9 +321,12 @@ static void sclp_memory_init(SCLPDevice *sclp)
      * down to align with the nearest increment boundary. */
     initial_mem = initial_mem >> increment_size << increment_size;

-    machine->ram_size = initial_mem;
-    /* let's propagate the changed ram size into the global variable. */
-    ram_size = initial_mem;
+    /* propagate the changed ram size into the different places */
+    if (initial_mem != machine->ram_size) {
+        machine->maxram_size -= machine->ram_size - initial_mem;
+        machine->ram_size = initial_mem;
+        ram_size = initial_mem;
+    }
 }

You would right now overwrite any maxmem setting (which might be ok as
we don't support it yet).

-- 

Thanks,

David / dhildenb