[Qemu-devel] [PATCH v3 2/2] s390x: Enable KVM huge page backing support

[Janosch Frank <frankja@linux.ibm.com>]

QEMU has had huge page support for a longer time already, but KVM
memory management under s390x needed some changes to work with huge
backings.

Now that we have support, let's enable it if requested and
available. Otherwise we now properly tell the user if there is no
support and back out instead of failing to run the VM later on.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
---
 target/s390x/kvm.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
index d923cf4240..f961c3b84a 100644
--- a/target/s390x/kvm.c
+++ b/target/s390x/kvm.c
@@ -34,6 +34,7 @@
 #include "qapi/error.h"
 #include "qemu/error-report.h"
 #include "qemu/timer.h"
+#include "qemu/mmap-alloc.h"
 #include "sysemu/sysemu.h"
 #include "sysemu/hw_accel.h"
 #include "hw/hw.h"
@@ -285,6 +286,20 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
 {
     MachineClass *mc = MACHINE_GET_CLASS(ms);
 
+    if (mem_path) {
+        if (qemu_mempath_getpagesize(mem_path) != (1 << 20)) {
+            error_report("Huge page backing with pages > 1M was specified, "
+                         "but KVM does not support this memory backing");
+            return -EINVAL;
+
+        }
+        if (kvm_vm_enable_cap(s, KVM_CAP_S390_HPAGE_1M, 0)) {
+            error_report("Huge page backing with 1M pages was specified, "
+                         "but KVM does not support this memory backing");
+            return -EINVAL;
+        }
+    }
+
     mc->default_cpu_type = S390_CPU_TYPE_NAME("host");
     cap_sync_regs = kvm_check_extension(s, KVM_CAP_SYNC_REGS);
     cap_async_pf = kvm_check_extension(s, KVM_CAP_ASYNC_PF);
-- 
2.14.3