Re: [PATCH v6 4/9] libxl: do not enable nested HVM unless global nested_hvm option enabled

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On 03/21/2018 10:32 AM, Marek Marczykowski-Górecki wrote:
Introduce global libxl option for enabling nested HVM feature, similar
to kvm module parameter. This will prevent enabling experimental feature
by mere presence of <cpu mode='host-passthrough'> element in domain
config, unless explicitly enabled. <cpu mode='host-passthrough'> element
may be used to configure other features, like NUMA, or CPUID.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Daniel P. Berrangé <berrange@xxxxxxxxxx>
---
Changes since v4:
  - add nested_hvm option to test_libvirtd_libxl.aug.in and libvirtd_libxl.aug
  - make it possible to override nested_hvm=0 with explicit <feature
    policy='require' name='vmx'/>
  - split xenconfig changes into separate commits
Changes since v3:
  - use config option nested_hvm, instead of requiring explicit <feature
    ...> entries
  - title changed from "libxl: do not enable nested HVM by mere presence
    of <cpu> element"
  - xenconfig: don't add <feature policy='force' name='vmx'/> since it is
    implied by presence of <cpu> element
  - xenconfig: produce <cpu> element even when converting on host not
    supporting vmx/svm, to not lose setting value
Changes since v2:
  - new patch
---
  src/libxl/libvirtd_libxl.aug         |  2 ++
  src/libxl/libxl.conf                 |  8 ++++++++
  src/libxl/libxl_conf.c               | 12 +++++++++++-
  src/libxl/libxl_conf.h               |  2 ++
  src/libxl/test_libvirtd_libxl.aug.in |  1 +
  tests/libxlxml2domconfigtest.c       |  3 +++
  6 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/src/libxl/libvirtd_libxl.aug b/src/libxl/libvirtd_libxl.aug
index b31cc07..58b9af3 100644
--- a/src/libxl/libvirtd_libxl.aug
+++ b/src/libxl/libvirtd_libxl.aug
@@ -28,12 +28,14 @@ module Libvirtd_libxl =
     let lock_entry = str_entry "lock_manager"
     let keepalive_interval_entry = int_entry "keepalive_interval"
     let keepalive_count_entry = int_entry "keepalive_count"
+   let nested_hvm_entry = bool_entry "nested_hvm"
(* Each entry in the config is one of the following ... *)
     let entry = autoballoon_entry
               | lock_entry
               | keepalive_interval_entry
               | keepalive_count_entry
+             | nested_hvm_entry
let comment = [ label "#comment" . del /#[ \t]*/ "# " . store /([^ \t\n][^\n]*)?/ . del /\n/ "\n" ]
     let empty = [ label "#empty" . eol ]
diff --git a/src/libxl/libxl.conf b/src/libxl/libxl.conf
index 264af7c..72825a7 100644
--- a/src/libxl/libxl.conf
+++ b/src/libxl/libxl.conf
@@ -41,3 +41,11 @@
  #
  #keepalive_interval = 5
  #keepalive_count = 5
+
+# Nested HVM default control. In order to use nested HVM feature, this option
+# needs to be enabled, in addition to specifying <cpu mode='host-passthrough'>
+# in domain configuration. This can be overridden in domain configuration by
+# explicitly setting <feature policy='require' name='vmx'/> inside <cpu/>
+# element.

Cool, the setting can be overridden by per-domain config.

+# By default it is disabled.
+#nested_hvm = 0
diff --git a/src/libxl/libxl_conf.c b/src/libxl/libxl_conf.c
index dcfdd67..3b9e828 100644
--- a/src/libxl/libxl_conf.c
+++ b/src/libxl/libxl_conf.c
@@ -360,7 +360,9 @@ libxlMakeDomBuildInfo(virDomainDefPtr def,
              bool hasHwVirt = false;
              bool svm = false, vmx = false;
- if (ARCH_IS_X86(def->os.arch)) {
+            /* enable nested HVM only if global nested_hvm option enable it and
+             * host support it*/
+            if (cfg->nested_hvm && ARCH_IS_X86(def->os.arch)) {
                  vmx = virCPUCheckFeature(caps->host.arch, caps->host.cpu, "vmx");
                  svm = virCPUCheckFeature(caps->host.arch, caps->host.cpu, "svm");
                  hasHwVirt = vmx | svm;

But IIUC this change will not allow per-domain config to override the global setting. If cfg->nested_hvm is false, svm and vmx are both false and FEATURE_REQUIRE is not honored.

Regards,
Jim

@@ -380,6 +382,11 @@ libxlMakeDomBuildInfo(virDomainDefPtr def,
case VIR_CPU_FEATURE_FORCE:
                          case VIR_CPU_FEATURE_REQUIRE:
+                            if ((vmx && STREQ(def->cpu->features[i].name, "vmx")) ||
+                                (svm && STREQ(def->cpu->features[i].name, "svm")))
+                                hasHwVirt = true;
+                            break;
+
                          case VIR_CPU_FEATURE_OPTIONAL:
                          case VIR_CPU_FEATURE_LAST:
                              break;
@@ -1699,6 +1706,9 @@ int libxlDriverConfigLoadFile(libxlDriverConfigPtr cfg,
      if (virConfGetValueUInt(conf, "keepalive_count", &cfg->keepAliveCount) < 0)
          goto cleanup;
+ if (virConfGetValueBool(conf, "nested_hvm", &cfg->nested_hvm) < 0)
+        goto cleanup;
+
      ret = 0;
cleanup:
diff --git a/src/libxl/libxl_conf.h b/src/libxl/libxl_conf.h
index ce9db26..27cfc1a 100644
--- a/src/libxl/libxl_conf.h
+++ b/src/libxl/libxl_conf.h
@@ -88,6 +88,8 @@ struct _libxlDriverConfig {
      int keepAliveInterval;
      unsigned int keepAliveCount;
+ bool nested_hvm;
+
      /* Once created, caps are immutable */
      virCapsPtr caps;
diff --git a/src/libxl/test_libvirtd_libxl.aug.in b/src/libxl/test_libvirtd_libxl.aug.in
index 63558e5..9106abe 100644
--- a/src/libxl/test_libvirtd_libxl.aug.in
+++ b/src/libxl/test_libvirtd_libxl.aug.in
@@ -6,3 +6,4 @@ module Test_libvirtd_libxl =
  { "lock_manager" = "lockd" }
  { "keepalive_interval" = "5" }
  { "keepalive_count" = "5" }
+{ "nested_hvm" = "1" }
diff --git a/tests/libxlxml2domconfigtest.c b/tests/libxlxml2domconfigtest.c
index cfbc37c..8819032 100644
--- a/tests/libxlxml2domconfigtest.c
+++ b/tests/libxlxml2domconfigtest.c
@@ -76,6 +76,9 @@ testCompareXMLToDomConfig(const char *xmlfile,
      if (!(log = (xentoollog_logger *)xtl_createlogger_stdiostream(stderr, XTL_DEBUG, 0)))
          goto cleanup;
+ /* for testing nested HVM */
+    cfg->nested_hvm = true;
+
      /* replace logger with stderr one */
      libxl_ctx_free(cfg->ctx);

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