[Qemu-devel] [PATCH v5] 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>
Reviewed-by: David Hildenbrand <david@redhat.com>
---

Now featuring all of the required braces.

---
 target/s390x/kvm.c | 35 +++++++++++++++++++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
index d923cf4240..8ba948c324 100644
--- a/target/s390x/kvm.c
+++ b/target/s390x/kvm.c
@@ -34,6 +34,8 @@
 #include "qapi/error.h"
 #include "qemu/error-report.h"
 #include "qemu/timer.h"
+#include "qemu/units.h"
+#include "qemu/mmap-alloc.h"
 #include "sysemu/sysemu.h"
 #include "sysemu/hw_accel.h"
 #include "hw/hw.h"
@@ -139,6 +141,7 @@ static int cap_mem_op;
 static int cap_s390_irq;
 static int cap_ri;
 static int cap_gs;
+static int cap_hpage_1m;
 
 static int active_cmma;
 
@@ -220,9 +223,9 @@ static void kvm_s390_enable_cmma(void)
         .attr = KVM_S390_VM_MEM_ENABLE_CMMA,
     };
 
-    if (mem_path) {
+    if (cap_hpage_1m) {
         warn_report("CMM will not be enabled because it is not "
-                    "compatible with hugetlbfs.");
+                    "compatible with huge memory backings.");
         return;
     }
     rc = kvm_vm_ioctl(kvm_state, KVM_SET_DEVICE_ATTR, &attr);
@@ -281,10 +284,38 @@ void kvm_s390_crypto_reset(void)
     }
 }
 
+static int kvm_s390_configure_mempath_backing(KVMState *s)
+{
+    size_t path_psize = qemu_mempath_getpagesize(mem_path);
+
+    if (path_psize == 4 * KiB) {
+        return 0;
+    }
+
+    if (path_psize != 1 * MiB) {
+        error_report("Memory backing with 2G pages 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("Memory backing with 1M pages was specified, "
+                     "but KVM does not support this memory backing");
+        return -EINVAL;
+    }
+
+    cap_hpage_1m = 1;
+    return 0;
+}
+
 int kvm_arch_init(MachineState *ms, KVMState *s)
 {
     MachineClass *mc = MACHINE_GET_CLASS(ms);
 
+    if (mem_path && kvm_s390_configure_mempath_backing(s)) {
+        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