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[libvirt] [PATCH] add flag to enforce hugepage backing of guest RAM



Add an element named "strict-hugepages" to control whether to 
refuse guest initialization in case hugepage allocation cannot 
be performed.

Signed-off-by: Marcelo Tosatti <mtosatti redhat com>

diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index ff50214..e79f5e6 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -632,6 +632,9 @@
       <dt><code>hugepages</code></dt>
       <dd>This tells the hypervisor that the guest should have its memory
         allocated using hugepages instead of the normal native page size.</dd>
+      <dt><code>strict-hugepages</code></dt>
+      <dd>This tells the hypervisor that the guest should refuse to start
+          in case of failure to allocate guest memory with hugepages</dd>
       <dt><code>nosharepages</code></dt>
       <dd>Instructs hypervisor to disable shared pages (memory merge, KSM) for
         this domain. <span class="since">Since 1.0.6</span></dd>
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 28e24f9..f16ef0b 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -11226,6 +11226,9 @@ virDomainDefParseXML(xmlDocPtr xml,
     if (virXPathBoolean("boolean(./memoryBacking/locked)", ctxt))
         def->mem.locked = true;
 
+    if ((node = virXPathNode("./memoryBacking/stricthugepages", ctxt)))
+        def->mem.strict_hugepages = true;
+
     /* Extract blkio cgroup tunables */
     if (virXPathUInt("string(./blkiotune/weight)", ctxt,
                      &def->blkio.weight) < 0)
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index d8f2e49..8ea5cf0 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -1977,6 +1977,7 @@ struct _virDomainDef {
         unsigned long long max_balloon; /* in kibibytes */
         unsigned long long cur_balloon; /* in kibibytes */
         bool hugepage_backed;
+        bool strict_hugepages;
         bool nosharepages;
         bool locked;
         int dump_core; /* enum virDomainMemDump */
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 96b8825..3f8d0a4 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -12133,10 +12133,9 @@ cleanup:
     return def;
 }
 
-
-static int qemuParseProcFileStrings(int pid_value,
-                                    const char *name,
-                                    char ***list)
+int qemuParseProcFileStrings(int pid_value,
+                             const char *name,
+                             char ***list)
 {
     char *path = NULL;
     int ret = -1;
diff --git a/src/qemu/qemu_command.h b/src/qemu/qemu_command.h
index de7683d..bcdfefa 100644
--- a/src/qemu/qemu_command.h
+++ b/src/qemu/qemu_command.h
@@ -226,7 +226,9 @@ virDomainDefPtr qemuParseCommandLinePid(virCapsPtr qemuCaps,
                                         char **pidfile,
                                         virDomainChrSourceDefPtr *monConfig,
                                         bool *monJSON);
-
+int qemuParseProcFileStrings(int pid_value,
+                             const char *name,
+                             char ***list);
 int qemuDomainAssignAddresses(virDomainDefPtr def,
                               virQEMUCapsPtr qemuCaps,
                               virDomainObjPtr obj)
diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index 8bcd98e..cb8298e 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -25,6 +25,7 @@
 #include <unistd.h>
 #include <signal.h>
 #include <sys/stat.h>
+#include <stdlib.h>
 #if defined(__linux__)
 # include <linux/capability.h>
 #elif defined(__FreeBSD__)
@@ -3507,6 +3508,95 @@ error:
 }
 
 
+/*
+ * Returns bool: whether to fail guest initialization.
+ *
+ */
+static bool qemuValidateStrictHugepage(virDomainObjPtr vm, virQEMUDriverConfigPtr cfg)
+{
+    bool ret = false;
+    char **maps = NULL;
+    int i;
+    char *buf;
+
+    if (!vm->def->mem.strict_hugepages)
+        return ret;
+
+    ret = true;
+
+    if (!vm->def->mem.hugepage_backed || !cfg->hugepagePath) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                _("strict huge pages depends on huge pages"));
+        return ret;
+    }
+
+    buf = malloc(strlen(cfg->hugepagePath) + 50);
+
+    /* The parser requires /proc/pid, which only exists on platforms
+     * like Linux where pid_t fits in int.  */
+    if ((int) vm->pid != vm->pid ||
+        qemuParseProcFileStrings(vm->pid, "maps", &maps) < 0)
+        goto cleanup;
+
+    for (i = 0; maps && maps[i]; i++) {
+        char *endptr;
+        unsigned long start, end;
+        const char *map = maps[i];
+        bool found = false;
+
+        sprintf(buf, "%s/qemu_back_mem.pc.ram.", cfg->hugepagePath);
+        if (strstr(map,buf) != NULL)
+            found = true;
+
+        sprintf(buf, "%s/kvm.", cfg->hugepagePath);
+        if (strstr(map,buf) != NULL)
+            found = true;
+
+        if (!found)
+            continue;
+
+        errno = 0;
+        start = strtol(map, &endptr, 16);
+        if ((errno == ERANGE && (start == LONG_MAX || start == LONG_MIN))
+                || (errno != 0 && start == 0)) {
+                continue;
+        }
+
+        if (endptr && *endptr == '-')
+            endptr++;
+
+        if (!*endptr)
+            continue;
+
+        errno = 0;
+        end = strtol(endptr, NULL, 16);
+        if ((errno == ERANGE && (end == LONG_MAX || end == LONG_MIN))
+                || (errno != 0 && end == 0)) {
+                continue;
+        }
+
+        if (end-start >= vm->def->mem.max_balloon * 1024) {
+            ret = false;
+            break;
+        }
+    }
+
+    if (ret) {
+        /* FIXME: is VIR_ERR_NO_MEMORY to be used exclusively
+         * to reference libvirt allocation failures?
+         */
+        virReportError(VIR_ERR_NO_MEMORY, "%s",
+                _("guest memory not hugetlbfs backed"));
+    }
+
+cleanup:
+    for (i = 0; maps && maps[i]; i++)
+        VIR_FREE(maps[i]);
+    free(buf);
+    return ret;
+}
+
+
 static bool
 qemuValidateCpuMax(virDomainDefPtr def, virQEMUCapsPtr qemuCaps)
 {
@@ -4071,6 +4161,13 @@ int qemuProcessStart(virConnectPtr conn,
             goto cleanup;
     }
 
+    /* enforce strict hugepage */
+    if (qemuValidateStrictHugepage(vm, cfg)) {
+        VIR_WARN("Failure to allocate hugepage backing for %s, exiting",
+                 vm->def->name);
+        goto cleanup;
+    }
+
     /* set default link states */
     /* qemu doesn't support setting this on the command line, so
      * enter the monitor */


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