[Xen-devel] [PATCH] x86/sysctl: Don't return cpu policy data for compiled-out support

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Policy objects aren't tiny, and the derivation logic isn't trivial.  We are
about to increase the number of policy objects, so take this opportunity to
drop logic and storage space based on CONFIG_{PV,HVM}.

Start by causing XEN_SYSCTL_get_cpu_policy to fail with -EOPNOTSUPP when
requesting data for a compiled-out subsystem.  Update xen-cpuid to cope and
continue to further system policies, seeing as the indicies are interleaved.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 tools/misc/xen-cpuid.c      |  9 +++++++++
 xen/arch/x86/sysctl.c       | 20 +++++++++++++++-----
 xen/include/public/sysctl.h |  2 ++
 3 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/tools/misc/xen-cpuid.c b/tools/misc/xen-cpuid.c
index 7726c4ed3c..f55b67640a 100644
--- a/tools/misc/xen-cpuid.c
+++ b/tools/misc/xen-cpuid.c
@@ -480,7 +480,16 @@ int main(int argc, char **argv)
 
                 if ( xc_get_system_cpu_policy(xch, i, &nr_leaves, leaves,
                                               &nr_msrs, msrs) )
+                {
+                    if ( errno == EOPNOTSUPP )
+                    {
+                        printf("%s policy not supported by Xen\n",
+                               sys_policies[i]);
+                        continue;
+                    }
+
                     err(1, "xc_get_system_cpu_policy(, %s,,)", 
sys_policies[i]);
+                }
 
                 print_policy(sys_policies[i], leaves, nr_leaves,
                              msrs, nr_msrs);
diff --git a/xen/arch/x86/sysctl.c b/xen/arch/x86/sysctl.c
index 4a76f0f47f..59a384023b 100644
--- a/xen/arch/x86/sysctl.c
+++ b/xen/arch/x86/sysctl.c
@@ -33,7 +33,7 @@
 #include <asm/psr.h>
 #include <asm/cpuid.h>
 
-const struct cpu_policy system_policies[] = {
+const struct cpu_policy system_policies[6] = {
     [ XEN_SYSCTL_cpu_policy_raw ] = {
         &raw_cpuid_policy,
         &raw_msr_policy,
@@ -42,22 +42,26 @@ const struct cpu_policy system_policies[] = {
         &host_cpuid_policy,
         &host_msr_policy,
     },
+#ifdef CONFIG_PV
     [ XEN_SYSCTL_cpu_policy_pv_max ] = {
         &pv_max_cpuid_policy,
         &pv_max_msr_policy,
     },
-    [ XEN_SYSCTL_cpu_policy_hvm_max ] = {
-        &hvm_max_cpuid_policy,
-        &hvm_max_msr_policy,
-    },
     [ XEN_SYSCTL_cpu_policy_pv_default ] = {
         &pv_max_cpuid_policy,
         &pv_max_msr_policy,
     },
+#endif
+#ifdef CONFIG_HVM
+    [ XEN_SYSCTL_cpu_policy_hvm_max ] = {
+        &hvm_max_cpuid_policy,
+        &hvm_max_msr_policy,
+    },
     [ XEN_SYSCTL_cpu_policy_hvm_default ] = {
         &hvm_max_cpuid_policy,
         &hvm_max_msr_policy,
     },
+#endif
 };
 
 struct l3_cache_info {
@@ -426,6 +430,12 @@ long arch_do_sysctl(
             array_index_nospec(sysctl->u.cpu_policy.index,
                                ARRAY_SIZE(system_policies))];
 
+        if ( !policy->cpuid || !policy->msr )
+        {
+            ret = -EOPNOTSUPP;
+            break;
+        }
+
         /* Process the CPUID leaves. */
         if ( guest_handle_is_null(sysctl->u.cpu_policy.cpuid_policy) )
             sysctl->u.cpu_policy.nr_leaves = CPUID_MAX_SERIALISED_LEAVES;
diff --git a/xen/include/public/sysctl.h b/xen/include/public/sysctl.h
index 7e43bfe1bd..4dfba39ed8 100644
--- a/xen/include/public/sysctl.h
+++ b/xen/include/public/sysctl.h
@@ -1051,6 +1051,8 @@ struct xen_sysctl_set_parameter {
  *               experimental features outside of security support.
  *  - Default_*: Default set of features a PV or HVM guest can use.  This is
  *               the security supported set.
+ * May fail with -EOPNOTSUPP if querying for PV or HVM data when support is
+ * compiled out of Xen.
  */
 struct xen_sysctl_cpu_policy {
 #define XEN_SYSCTL_cpu_policy_raw          0
-- 
2.11.0


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