kvm: Allow to set shadow MMU size

Introduce the KVM-specific machine option kvm_shadow_mem. It allows to
set a custom shadow MMU size for the virtual machine. This is useful for
stress testing e.g.

Only x86 supports this for now, but it is in principle a generic
concept for all targets with shadow MMUs.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>

qemu-config.c

@@ -535,6 +535,10 @@ static QemuOptsList qemu_machine_opts = {
             .name = "kernel_irqchip",
             .type = QEMU_OPT_BOOL,
             .help = "use KVM in-kernel irqchip",
+        }, {
+            .name = "kvm_shadow_mem",
+            .type = QEMU_OPT_SIZE,
+            .help = "KVM shadow MMU size",
         },
         { /* End of list */ }
     },

qemu-options.hx

@@ -32,7 +32,8 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \
     "                selects emulated machine (-machine ? for list)\n"
     "                property accel=accel1[:accel2[:...]] selects accelerator\n"
     "                supported accelerators are kvm, xen, tcg (default: tcg)\n"
-    "                kernel_irqchip=on|off controls accelerated irqchip support\n",
+    "                kernel_irqchip=on|off controls accelerated irqchip support\n"
+    "                kvm_shadow_mem=size of KVM shadow MMU\n",
     QEMU_ARCH_ALL)
 STEXI
 @item -machine [type=]@var{name}[,prop=@var{value}[,...]]
@@ -47,6 +48,8 @@ than one accelerator specified, the next one is used if the previous one fails
 to initialize.
 @item kernel_irqchip=on|off
 Enables in-kernel irqchip support for the chosen accelerator when available.
+@item kvm_shadow_mem=size
+Defines the size of the KVM shadow MMU.
 @end table
 ETEXI
 

target-i386/kvm.c

@@ -646,7 +646,9 @@ static int kvm_get_supported_msrs(KVMState *s)
 
 int kvm_arch_init(KVMState *s)
 {
+    QemuOptsList *list = qemu_find_opts("machine");
     uint64_t identity_base = 0xfffbc000;
+    uint64_t shadow_mem;
     int ret;
     struct utsname utsname;
 
@@ -693,6 +695,17 @@ int kvm_arch_init(KVMState *s)
     }
     qemu_register_reset(kvm_unpoison_all, NULL);
 
+    if (!QTAILQ_EMPTY(&list->head)) {
+        shadow_mem = qemu_opt_get_size(QTAILQ_FIRST(&list->head),
+                                       "kvm_shadow_mem", -1);
+        if (shadow_mem != -1) {
+            shadow_mem /= 4096;
+            ret = kvm_vm_ioctl(s, KVM_SET_NR_MMU_PAGES, shadow_mem);
+            if (ret < 0) {
+                return ret;
+            }
+        }
+    }
     return 0;
 }