spapr: Use maximum page size capability to simplify memory backend checking

The way we used to handle KVM allowable guest pagesizes for PAPR guests
required some convoluted checking of memory attached to the guest.

The allowable pagesizes advertised to the guest cpus depended on the memory
which was attached at boot, but then we needed to ensure that any memory
later hotplugged didn't change which pagesizes were allowed.

Now that we have an explicit machine option to control the allowable
maximum pagesize we can simplify this.  We just check all memory backends
against that declared pagesize.  We check base and cold-plugged memory at
reset time, and hotplugged memory at pre_plug() time.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Greg Kurz <groug@kaod.org>

hw/ppc/spapr.c

@@ -3192,11 +3192,13 @@ static void spapr_memory_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
                                   Error **errp)
 {
     const sPAPRMachineClass *smc = SPAPR_MACHINE_GET_CLASS(hotplug_dev);
+    sPAPRMachineState *spapr = SPAPR_MACHINE(hotplug_dev);
     PCDIMMDevice *dimm = PC_DIMM(dev);
     PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(dimm);
     MemoryRegion *mr;
     uint64_t size;
-    char *mem_dev;
+    Object *memdev;
+    hwaddr pagesize;
 
     if (!smc->dr_lmb_enabled) {
         error_setg(errp, "Memory hotplug not supported for this machine");
@@ -3215,15 +3217,10 @@ static void spapr_memory_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
         return;
     }
 
-    mem_dev = object_property_get_str(OBJECT(dimm), PC_DIMM_MEMDEV_PROP, NULL);
-    if (mem_dev && !kvmppc_is_mem_backend_page_size_ok(mem_dev)) {
-        error_setg(errp, "Memory backend has bad page size. "
-                   "Use 'memory-backend-file' with correct mem-path.");
-        goto out;
-    }
-
-out:
-    g_free(mem_dev);
+    memdev = object_property_get_link(OBJECT(dimm), PC_DIMM_MEMDEV_PROP,
+                                      &error_abort);
+    pagesize = host_memory_backend_pagesize(MEMORY_BACKEND(memdev));
+    spapr_check_pagesize(spapr, pagesize, errp);
 }
 
 struct sPAPRDIMMState {

hw/ppc/spapr_caps.c

@@ -26,6 +26,7 @@
 #include "qapi/error.h"
 #include "qapi/visitor.h"
 #include "sysemu/hw_accel.h"
+#include "exec/ram_addr.h"
 #include "target/ppc/cpu.h"
 #include "target/ppc/mmu-hash64.h"
 #include "cpu-models.h"
@@ -304,14 +305,34 @@ static void cap_safe_indirect_branch_apply(sPAPRMachineState *spapr,
 
 #define VALUE_DESC_TRISTATE     " (broken, workaround, fixed)"
 
+void spapr_check_pagesize(sPAPRMachineState *spapr, hwaddr pagesize,
+                          Error **errp)
+{
+    hwaddr maxpagesize = (1ULL << spapr->eff.caps[SPAPR_CAP_HPT_MAXPAGESIZE]);
+
+    if (!kvmppc_hpt_needs_host_contiguous_pages()) {
+        return;
+    }
+
+    if (maxpagesize > pagesize) {
+        error_setg(errp,
+                   "Can't support %"HWADDR_PRIu" kiB guest pages with %"
+                   HWADDR_PRIu" kiB host pages with this KVM implementation",
+                   maxpagesize >> 10, pagesize >> 10);
+    }
+}
+
 static void cap_hpt_maxpagesize_apply(sPAPRMachineState *spapr,
                                       uint8_t val, Error **errp)
 {
     if (val < 12) {
         error_setg(errp, "Require at least 4kiB hpt-max-page-size");
+        return;
     } else if (val < 16) {
         warn_report("Many guests require at least 64kiB hpt-max-page-size");
     }
+
+    spapr_check_pagesize(spapr, qemu_getrampagesize(), errp);
 }
 
 sPAPRCapabilityInfo capability_table[SPAPR_CAP_NUM] = {

include/hw/ppc/spapr.h

@@ -806,4 +806,7 @@ void spapr_caps_cpu_apply(sPAPRMachineState *spapr, PowerPCCPU *cpu);
 void spapr_caps_add_properties(sPAPRMachineClass *smc, Error **errp);
 int spapr_caps_post_migration(sPAPRMachineState *spapr);
 
+void spapr_check_pagesize(sPAPRMachineState *spapr, hwaddr pagesize,
+                          Error **errp);
+
 #endif /* HW_SPAPR_H */

target/ppc/kvm.c

@@ -500,26 +500,12 @@ static void kvm_fixup_page_sizes(PowerPCCPU *cpu)
         cpu->hash64_opts->flags &= ~PPC_HASH64_1TSEG;
     }
 }
-
-bool kvmppc_is_mem_backend_page_size_ok(const char *obj_path)
-{
-    Object *mem_obj = object_resolve_path(obj_path, NULL);
-    long pagesize = host_memory_backend_pagesize(MEMORY_BACKEND(mem_obj));
-
-    return pagesize >= max_cpu_page_size;
-}
-
 #else /* defined (TARGET_PPC64) */
 
 static inline void kvm_fixup_page_sizes(PowerPCCPU *cpu)
 {
 }
 
-bool kvmppc_is_mem_backend_page_size_ok(const char *obj_path)
-{
-    return true;
-}
-
 #endif /* !defined (TARGET_PPC64) */
 
 unsigned long kvm_arch_vcpu_id(CPUState *cpu)

target/ppc/kvm_ppc.h

@@ -71,7 +71,6 @@ int kvmppc_resize_hpt_commit(PowerPCCPU *cpu, target_ulong flags, int shift);
 bool kvmppc_pvr_workaround_required(PowerPCCPU *cpu);
 
 bool kvmppc_hpt_needs_host_contiguous_pages(void);
-bool kvmppc_is_mem_backend_page_size_ok(const char *obj_path);
 
 #else
 
@@ -228,11 +227,6 @@ static inline bool kvmppc_hpt_needs_host_contiguous_pages(void)
     return false;
 }
 
-static inline bool kvmppc_is_mem_backend_page_size_ok(const char *obj_path)
-{
-    return true;
-}
-
 static inline bool kvmppc_has_cap_spapr_vfio(void)
 {
     return false;