[PATCH] add option to enforce minimal pagesize for hugetlbfs backed guests

[Marcelo Tosatti <mtosatti@xxxxxxxxxx>]

Require a minimal pagesize for hugetlbfs backed guests. Fail guest initialization
if hugetlbfs mount is configured with smaller page size.

Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>

diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index fd02864..e28d182 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -632,6 +632,10 @@
       <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>pagesize</code></dt>
+      <dd>This tells the hypervisor that the guest should refuse to start
+          in case of failure to allocate guest memory with hugepages equal
+          to or larger than the specified size</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..babb745 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -11274,6 +11274,10 @@ virDomainDefParseXML(xmlDocPtr xml,
                              &def->mem.swap_hard_limit, false) < 0)
         goto error;
 
+    if (virDomainParseMemory("./memoryBacking/hugepages/pagesize[1]", ctxt,
+                             &def->mem.page_size, false) < 0)
+        goto error;
+
     n = virXPathULong("string(./vcpu[1])", ctxt, &count);
     if (n == -2) {
         virReportError(VIR_ERR_XML_ERROR, "%s",
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index d8f2e49..03a900d 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -1984,6 +1984,7 @@ struct _virDomainDef {
         unsigned long long soft_limit; /* in kibibytes */
         unsigned long long min_guarantee; /* in kibibytes */
         unsigned long long swap_hard_limit; /* in kibibytes */
+        unsigned long long page_size; /* in kibibytes */
     } mem;
     unsigned short vcpus;
     unsigned short maxvcpus;
diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index 8bcd98e..cd5e1c8 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -3570,6 +3570,33 @@ cleanup:
     return ret;
 }
 
+#ifdef __linux__
+
+#include <sys/vfs.h>
+
+#define HUGETLBFS_MAGIC       0x958458f6
+
+static long gethugepagesize(const char *path)
+{
+    struct statfs fs;
+    int ret;
+
+    do {
+        ret = statfs(path, &fs);
+    } while (ret != 0 && errno == EINTR);
+
+    if (ret != 0) {
+        perror(path);
+        return 0;
+    }
+
+    if (fs.f_type != HUGETLBFS_MAGIC)
+        return 0;
+
+    return fs.f_bsize;
+}
+#endif
+
 
 int qemuProcessStart(virConnectPtr conn,
                      virQEMUDriverPtr driver,
@@ -3712,6 +3739,31 @@ int qemuProcessStart(virConnectPtr conn,
                     "%s", _("Unable to set huge path in security driver"));
             goto cleanup;
         }
+
+        if (vm->def->mem.page_size) {
+#ifdef __linux__
+            unsigned long hpagesize = gethugepagesize(cfg->hugepagePath);
+
+            if (!hpagesize) {
+                virReportError(VIR_ERR_INTERNAL_ERROR,
+                               "%s", _("Unable to stat hugepage path"));
+                goto cleanup;
+            }
+
+            hpagesize /= 1024;
+
+            if (hpagesize < vm->def->mem.page_size) {
+                    virReportError(VIR_ERR_INTERNAL_ERROR,
+                    _("Error: hugetlbfs page size=%ld < pagesize=%lld"),
+                    hpagesize, vm->def->mem.page_size);
+                goto cleanup;
+            }
+#else
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       "%s", _("pagesize option unsupported"));
+        goto cleanup;
+#endif
+        }
     }
 
     /* Ensure no historical cgroup for this VM is lying around bogus

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