[Qemu-devel] [PATCH v4] Add option to mlock qemu and guest memory

[Satoru Moriya]

In certain scenario, latency induced by paging is significant and
memory locking is needed. Also, in the scenario with untrusted
guests, latency improvement due to mlock is desired.

This patch introduces a following new option to mlock guest and
qemu memory:

-realtime mlock=on|off

Signed-off-by: Satoru Moriya <address@hidden>
Reviewed-by: Paolo Bonzini <address@hidden>
Reviewed-by: Marcelo Tosatti <address@hidden>
---
ChangeLog:
v4
 - Update commit message
v3
 - Modify os_mlock() to return error code
 - Update configure_realtime() to handle return value from os_mlock()
 - Change the variable name from is_mlock to enable_mlock in 
configure_realtime()
 - Rebase qemu version 1.4.50

v2
 - Change option name from -mlock to -realtime mlock=on|off
 - Rebase qemu version 1.3.91
 - Update patch description

 include/sysemu/os-posix.h |  1 +
 include/sysemu/os-win32.h |  5 +++++
 os-posix.c                | 12 ++++++++++++
 qemu-options.hx           | 13 +++++++++++++
 vl.c                      | 34 ++++++++++++++++++++++++++++++++++
 5 files changed, 65 insertions(+)

diff --git a/include/sysemu/os-posix.h b/include/sysemu/os-posix.h
index 7f198e4..25d0b2a 100644
--- a/include/sysemu/os-posix.h
+++ b/include/sysemu/os-posix.h
@@ -31,6 +31,7 @@ void os_set_proc_name(const char *s);
 void os_setup_signal_handling(void);
 void os_daemonize(void);
 void os_setup_post(void);
+int os_mlock(void);
 
 typedef struct timeval qemu_timeval;
 #define qemu_gettimeofday(tp) gettimeofday(tp, NULL)
diff --git a/include/sysemu/os-win32.h b/include/sysemu/os-win32.h
index 71f5fa0..bf8523a 100644
--- a/include/sysemu/os-win32.h
+++ b/include/sysemu/os-win32.h
@@ -106,4 +106,9 @@ static inline bool is_daemonized(void)
     return false;
 }
 
+static inline int os_mlock(void)
+{
+    return -ENOSYS;
+}
+
 #endif
diff --git a/os-posix.c b/os-posix.c
index 5c64518..d39261d 100644
--- a/os-posix.c
+++ b/os-posix.c
@@ -363,3 +363,15 @@ bool is_daemonized(void)
 {
     return daemonize;
 }
+
+int os_mlock(void)
+{
+    int ret = 0;
+
+    ret = mlockall(MCL_CURRENT | MCL_FUTURE);
+    if (ret < 0) {
+        perror("mlockall");
+    }
+
+    return ret;
+}
diff --git a/qemu-options.hx b/qemu-options.hx
index 06dd565..1ec9541 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -2569,6 +2569,19 @@ STEXI
 Do not start CPU at startup (you must type 'c' in the monitor).
 ETEXI
 
+DEF("realtime", HAS_ARG, QEMU_OPTION_realtime,
+    "-realtime [mlock=on|off]\n"
+    "                run qemu with realtime features\n"
+    "                mlock=on|off controls mlock support (default: on)\n",
+    QEMU_ARCH_ALL)
+STEXI
address@hidden -realtime mlock=on|off
address@hidden -realtime
+Run qemu with realtime features.
+mlocking qemu and guest memory can be enabled via @option{mlock=on}
+(enabled by default).
+ETEXI
+
 DEF("gdb", HAS_ARG, QEMU_OPTION_gdb, \
     "-gdb dev        wait for gdb connection on 'dev'\n", QEMU_ARCH_ALL)
 STEXI
diff --git a/vl.c b/vl.c
index aeed7f4..71bbcf1 100644
--- a/vl.c
+++ b/vl.c
@@ -521,6 +521,18 @@ static QemuOptsList qemu_tpmdev_opts = {
     },
 };
 
+static QemuOptsList qemu_realtime_opts = {
+    .name = "realtime",
+    .head = QTAILQ_HEAD_INITIALIZER(qemu_realtime_opts.head),
+    .desc = {
+        {
+            .name = "mlock",
+            .type = QEMU_OPT_BOOL,
+        },
+        { /* end of list */ }
+    },
+};
+
 const char *qemu_get_vm_name(void)
 {
     return qemu_name;
@@ -1420,6 +1432,20 @@ static void smp_parse(const char *optarg)
         max_cpus = smp_cpus;
 }
 
+static void configure_realtime(QemuOpts *opts)
+{
+    bool enable_mlock;
+
+    enable_mlock = qemu_opt_get_bool(opts, "mlock", true);
+
+    if (enable_mlock) {
+        if (os_mlock() < 0) {
+            fprintf(stderr, "qemu: locking memory failed\n");
+            exit(1);
+        }
+    }
+}
+
 /***********************************************************/
 /* USB devices */
 
@@ -2909,6 +2935,7 @@ int main(int argc, char **argv, char **envp)
     qemu_add_opts(&qemu_add_fd_opts);
     qemu_add_opts(&qemu_object_opts);
     qemu_add_opts(&qemu_tpmdev_opts);
+    qemu_add_opts(&qemu_realtime_opts);
 
     runstate_init();
 
@@ -3878,6 +3905,13 @@ int main(int argc, char **argv, char **envp)
                     exit(1);
                 }
                 break;
+            case QEMU_OPTION_realtime:
+                opts = qemu_opts_parse(qemu_find_opts("realtime"), optarg, 0);
+                if (!opts) {
+                    exit(1);
+                }
+                configure_realtime(opts);
+                break;
             default:
                 os_parse_cmd_args(popt->index, optarg);
             }
-- 
1.7.11.7