Re: [PATCH v1 2/8] x86/xen: simplify xen_oldmem_pfn_is_ram()

On 9/29/21 5:03 AM, David Hildenbrand wrote:

On 29.09.21 10:45, David Hildenbrand wrote:

quoted

quoted

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.

quoted

   }
   #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

quoted

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

so this is a good thing ;-)


-boris

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