PPC: sPAPR: Only use getpagesize() when we run with kvm

We currently size the msi window trap page according to the host's page
size so that we poke a working hole into a memory slot in case we overlap.

However, this is only ever necessary with KVM active. Without KVM, we should
rather try to be host platform agnostic and use a constant size: 4k.

This fixes a build breakage on win32 hosts.
Signed-off-by: NAlexander Graf <agraf@suse.de>

hw/ppc/spapr_pci.c

@@ -469,6 +469,8 @@ static const MemoryRegionOps spapr_msi_ops = {
 
 void spapr_pci_msi_init(sPAPREnvironment *spapr, hwaddr addr)
 {
+    uint64_t window_size = 4096;
+
     /*
      * As MSI/MSIX interrupts trigger by writing at MSI/MSIX vectors,
      * we need to allocate some memory to catch those writes coming
@@ -476,10 +478,19 @@ void spapr_pci_msi_init(sPAPREnvironment *spapr, hwaddr addr)
      * As MSIMessage:addr is going to be the same and MSIMessage:data
      * is going to be a VIRQ number, 4 bytes of the MSI MR will only
      * be used.
+     *
+     * For KVM we want to ensure that this memory is a full page so that
+     * our memory slot is of page size granularity.
      */
+#ifdef CONFIG_KVM
+    if (kvm_enabled()) {
+        window_size = getpagesize();
+    }
+#endif
+
     spapr->msi_win_addr = addr;
     memory_region_init_io(&spapr->msiwindow, NULL, &spapr_msi_ops, spapr,
-                          "msi", getpagesize());
+                          "msi", window_size);
     memory_region_add_subregion(get_system_memory(), spapr->msi_win_addr,
                                 &spapr->msiwindow);
 }