[Xen-devel] [PATCH] x86/libxl: choose a sane default for HAP

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Current libxl code will always enable Hardware Assisted Paging (HAP),
expecting that the hypervisor will fallback to shadow if HAP is not
available. With the changes to the domain builder that's not the case
any longer, and the hypervisor will raise an error if HAP is not
available instead of silently falling back to shadow.

In order to keep the previous functionality report whether HAP is
available or not in XEN_SYSCTL_physinfo, so that the toolstack can
select a sane default if there's no explicit user selection of whether
HAP should be used.

Fixes: d0c0ba7d3de ('x86/hvm/domain: remove the 'hap_enabled' flag')
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Cc: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
---
 tools/libxl/libxl.c         |  1 +
 tools/libxl/libxl_arch.h    |  4 ++--
 tools/libxl/libxl_arm.c     |  7 +++++--
 tools/libxl/libxl_create.c  | 10 ++++++----
 tools/libxl/libxl_types.idl |  1 +
 tools/libxl/libxl_x86.c     | 15 +++++++++++++--
 xen/arch/x86/sysctl.c       |  2 ++
 xen/include/public/sysctl.h |  4 ++++
 8 files changed, 34 insertions(+), 10 deletions(-)

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index ec71574e99..5c0fcf320e 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -399,6 +399,7 @@ int libxl_get_physinfo(libxl_ctx *ctx, libxl_physinfo 
*physinfo)
     physinfo->cap_pv = !!(xcphysinfo.capabilities & XEN_SYSCTL_PHYSCAP_pv);
     physinfo->cap_hvm_directio =
         !!(xcphysinfo.capabilities & XEN_SYSCTL_PHYSCAP_directio);
+    physinfo->cap_hap = !!(xcphysinfo.capabilities & XEN_SYSCTL_PHYSCAP_hap);
 
     GC_FREE;
     return 0;
diff --git a/tools/libxl/libxl_arch.h b/tools/libxl/libxl_arch.h
index d624159e53..3f59e790b7 100644
--- a/tools/libxl/libxl_arch.h
+++ b/tools/libxl/libxl_arch.h
@@ -65,8 +65,8 @@ _hidden
 int libxl__arch_domain_map_irq(libxl__gc *gc, uint32_t domid, int irq);
 
 _hidden
-void libxl__arch_domain_create_info_setdefault(libxl__gc *gc,
-                                               libxl_domain_create_info 
*c_info);
+int libxl__arch_domain_create_info_setdefault(libxl__gc *gc,
+                                              libxl_domain_create_info 
*c_info);
 
 _hidden
 void libxl__arch_domain_build_info_setdefault(libxl__gc *gc,
diff --git a/tools/libxl/libxl_arm.c b/tools/libxl/libxl_arm.c
index 141e159043..b067869154 100644
--- a/tools/libxl/libxl_arm.c
+++ b/tools/libxl/libxl_arm.c
@@ -1114,8 +1114,8 @@ int libxl__arch_domain_map_irq(libxl__gc *gc, uint32_t 
domid, int irq)
     return xc_domain_bind_pt_spi_irq(CTX->xch, domid, irq, irq);
 }
 
-void libxl__arch_domain_create_info_setdefault(libxl__gc *gc,
-                                               libxl_domain_create_info 
*c_info)
+int libxl__arch_domain_create_info_setdefault(libxl__gc *gc,
+                                              libxl_domain_create_info *c_info)
 {
     /*
      * Arm guest are now considered as PVH by the toolstack. To allow
@@ -1130,6 +1130,9 @@ void libxl__arch_domain_create_info_setdefault(libxl__gc 
*gc,
         c_info->type = LIBXL_DOMAIN_TYPE_PVH;
         /* All other fields can remain untouched */
     }
+    libxl_defbool_setdefault(&c_info->hap, true);
+
+    return 0;
 }
 
 void libxl__arch_domain_build_info_setdefault(libxl__gc *gc,
diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index 03ce166f4f..431ead2067 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -30,17 +30,19 @@
 int libxl__domain_create_info_setdefault(libxl__gc *gc,
                                          libxl_domain_create_info *c_info)
 {
+    int rc;
+
     if (!c_info->type) {
         LOG(ERROR, "domain type unspecified");
         return ERROR_INVAL;
     }
 
-    libxl__arch_domain_create_info_setdefault(gc, c_info);
+    rc = libxl__arch_domain_create_info_setdefault(gc, c_info);
+    if (rc)
+        return rc;
 
-    if (c_info->type != LIBXL_DOMAIN_TYPE_PV) {
-        libxl_defbool_setdefault(&c_info->hap, true);
+    if (c_info->type != LIBXL_DOMAIN_TYPE_PV)
         libxl_defbool_setdefault(&c_info->oos, true);
-    }
 
     libxl_defbool_setdefault(&c_info->run_hotplug_scripts, true);
     libxl_defbool_setdefault(&c_info->driver_domain, false);
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index b61399ce36..9e1f8515d3 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -1025,6 +1025,7 @@ libxl_physinfo = Struct("physinfo", [
     ("cap_hvm", bool),
     ("cap_pv", bool),
     ("cap_hvm_directio", bool), # No longer HVM specific
+    ("cap_hap", bool),
     ], dir=DIR_OUT)
 
 libxl_connectorinfo = Struct("connectorinfo", [
diff --git a/tools/libxl/libxl_x86.c b/tools/libxl/libxl_x86.c
index c0f88a7eaa..bdc9d9adfe 100644
--- a/tools/libxl/libxl_x86.c
+++ b/tools/libxl/libxl_x86.c
@@ -620,9 +620,20 @@ int libxl__arch_domain_finalise_hw_description(libxl__gc 
*gc,
     return rc;
 }
 
-void libxl__arch_domain_create_info_setdefault(libxl__gc *gc,
-                                               libxl_domain_create_info 
*c_info)
+int libxl__arch_domain_create_info_setdefault(libxl__gc *gc,
+                                              libxl_domain_create_info *c_info)
 {
+    libxl_physinfo pi;
+    int rc = libxl_get_physinfo(CTX, &pi);
+
+    if (rc) {
+        LOG(ERROR, "unable to get physinfo");
+        return rc;
+    }
+
+    libxl_defbool_setdefault(&c_info->hap, pi.cap_hap);
+
+    return 0;
 }
 
 void libxl__arch_domain_build_info_setdefault(libxl__gc *gc,
diff --git a/xen/arch/x86/sysctl.c b/xen/arch/x86/sysctl.c
index c50d910a1c..74ea184087 100644
--- a/xen/arch/x86/sysctl.c
+++ b/xen/arch/x86/sysctl.c
@@ -165,6 +165,8 @@ void arch_do_physinfo(struct xen_sysctl_physinfo *pi)
         pi->capabilities |= XEN_SYSCTL_PHYSCAP_pv;
     if ( iommu_enabled )
         pi->capabilities |= XEN_SYSCTL_PHYSCAP_directio;
+    if ( hvm_hap_supported() )
+        pi->capabilities |= XEN_SYSCTL_PHYSCAP_hap;
 }
 
 long arch_do_sysctl(
diff --git a/xen/include/public/sysctl.h b/xen/include/public/sysctl.h
index 91c48dcae0..6c457625e9 100644
--- a/xen/include/public/sysctl.h
+++ b/xen/include/public/sysctl.h
@@ -90,6 +90,10 @@ struct xen_sysctl_tbuf_op {
  /* (x86) The platform supports direct access to I/O devices with IOMMU. */
 #define _XEN_SYSCTL_PHYSCAP_directio     2
 #define XEN_SYSCTL_PHYSCAP_directio  (1u<<_XEN_SYSCTL_PHYSCAP_directio)
+/* (x86) The platform supports Hardware Assisted Paging. */
+#define _XEN_SYSCTL_PHYSCAP_hap          3
+#define XEN_SYSCTL_PHYSCAP_hap           (1u<<_XEN_SYSCTL_PHYSCAP_hap)
+
 struct xen_sysctl_physinfo {
     uint32_t threads_per_core;
     uint32_t cores_per_socket;
-- 
2.22.0


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