Linux Virtualization - Sep 2021 - [PATCH v1 2/8] x86/xen: simplify xen_oldmem_pfn_is_ram()

On 29.09.21 10:45, David Hildenbrand wrote:
>>
>> How about
>>
>>   ??? return a.mem_type != HVMMEM_mmio_dm;
>>
> 
> Ha, how could I have missed that :)
> 
>>
>> Result should be promoted to int and this has added benefit of not
requiring changes in patch 4.
>>
> 
> Can we go one step further and do
> 
> 
> @@ -20,24 +20,11 @@ static int xen_oldmem_pfn_is_ram(unsigned long pfn)
>           struct xen_hvm_get_mem_type a = {
>                   .domid = DOMID_SELF,
>                   .pfn = pfn,
> +               .mem_type = HVMMEM_ram_rw,
>           };
> -       int ram;
>    
> -       if (HYPERVISOR_hvm_op(HVMOP_get_mem_type, &a))
> -               return -ENXIO;
> -
> -       switch (a.mem_type) {
> -       case HVMMEM_mmio_dm:
> -               ram = 0;
> -               break;
> -       case HVMMEM_ram_rw:
> -       case HVMMEM_ram_ro:
> -       default:
> -               ram = 1;
> -               break;
> -       }
> -
> -       return ram;
> +       HYPERVISOR_hvm_op(HVMOP_get_mem_type, &a);
> +       return a.mem_type != HVMMEM_mmio_dm;
>    }
>    #endif
> 
> 
> Assuming that if HYPERVISOR_hvm_op() fails that
> .mem_type is not set to HVMMEM_mmio_dm.
> 
Okay we can't, due to "__must_check" ...

-- 
Thanks,

David / dhildenb

On 9/29/21 5:03 AM, David Hildenbrand wrote:
> On 29.09.21 10:45, David Hildenbrand wrote:
>>>
>> Can we go one step further and do
>>
>>
>> @@ -20,24 +20,11 @@ static int xen_oldmem_pfn_is_ram(unsigned long pfn)
>> ????????? struct xen_hvm_get_mem_type a = {
>> ????????????????? .domid = DOMID_SELF,
>> ????????????????? .pfn = pfn,
>> +?????????????? .mem_type = HVMMEM_ram_rw,
>> ????????? };
>> -?????? int ram;
>> ?? -?????? if (HYPERVISOR_hvm_op(HVMOP_get_mem_type, &a))
>> -?????????????? return -ENXIO;
>> -
>> -?????? switch (a.mem_type) {
>> -?????? case HVMMEM_mmio_dm:
>> -?????????????? ram = 0;
>> -?????????????? break;
>> -?????? case HVMMEM_ram_rw:
>> -?????? case HVMMEM_ram_ro:
>> -?????? default:
>> -?????????????? ram = 1;
>> -?????????????? break;
>> -?????? }
>> -
>> -?????? return ram;
>> +?????? HYPERVISOR_hvm_op(HVMOP_get_mem_type, &a);
>> +?????? return a.mem_type != HVMMEM_mmio_dm;

I was actually thinking of asking you to add another patch with pr_warn_once()
here (and print error code as well). This call failing is indication of
something going quite wrong and it would be good to know about this.

>> ?? }
>> ?? #endif
>>
>>
>> Assuming that if HYPERVISOR_hvm_op() fails that
>> .mem_type is not set to HVMMEM_mmio_dm.

I don't think we can assume that argument described as OUT in the ABI will
not be clobbered in case of error

>>
>
> Okay we can't, due to "__must_check" ...

so this is a good thing ;-)


-boris