[PATCH 03/13] libs/guest: allow fetching a specific CPUID leaf from a cpu policy

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

Introduce an interface that returns a specific leaf/subleaf from a cpu
policy in xen_cpuid_leaf_t format.

This is useful to callers can peek data from the opaque
xc_cpu_policy_t type.

No caller of the interface introduced on this patch.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Changes since v6:
 - Add newline before return.

Changes since v5:
 - Zero out parameter.

Changes since v3:
 - Use x86_cpuid_get_leaf.

Changes since v1:
 - Use find leaf.
---
 tools/include/xenguest.h        |  3 +++
 tools/libs/guest/xg_cpuid_x86.c | 26 ++++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/tools/include/xenguest.h b/tools/include/xenguest.h
index e01f494b772a..0a6fd9930627 100644
--- a/tools/include/xenguest.h
+++ b/tools/include/xenguest.h
@@ -807,6 +807,9 @@ int xc_cpu_policy_update_cpuid(xc_interface *xch, 
xc_cpu_policy_t *policy,
                                uint32_t nr);
 int xc_cpu_policy_update_msrs(xc_interface *xch, xc_cpu_policy_t *policy,
                               const xen_msr_entry_t *msrs, uint32_t nr);
+int xc_cpu_policy_get_cpuid(xc_interface *xch, const xc_cpu_policy_t *policy,
+                            uint32_t leaf, uint32_t subleaf,
+                            xen_cpuid_leaf_t *out);
 
 /* Compatibility calculations. */
 bool xc_cpu_policy_is_compatible(xc_interface *xch, xc_cpu_policy_t *host,
diff --git a/tools/libs/guest/xg_cpuid_x86.c b/tools/libs/guest/xg_cpuid_x86.c
index 67e0dc9b4ad2..630d0018529f 100644
--- a/tools/libs/guest/xg_cpuid_x86.c
+++ b/tools/libs/guest/xg_cpuid_x86.c
@@ -828,6 +828,32 @@ int xc_cpu_policy_update_msrs(xc_interface *xch, 
xc_cpu_policy_t *policy,
     return rc;
 }
 
+int xc_cpu_policy_get_cpuid(xc_interface *xch, const xc_cpu_policy_t *policy,
+                            uint32_t leaf, uint32_t subleaf,
+                            xen_cpuid_leaf_t *out)
+{
+    const struct cpuid_leaf *tmp;
+
+    *out = (xen_cpuid_leaf_t){};
+
+    tmp = x86_cpuid_get_leaf(&policy->policy, leaf, subleaf);
+    if ( !tmp )
+    {
+        /* Unable to find a matching leaf. */
+        errno = ENOENT;
+        return -1;
+    }
+
+    out->leaf = leaf;
+    out->subleaf = subleaf;
+    out->a = tmp->a;
+    out->b = tmp->b;
+    out->c = tmp->c;
+    out->d = tmp->d;
+
+    return 0;
+}
+
 bool xc_cpu_policy_is_compatible(xc_interface *xch, xc_cpu_policy_t *host,
                                  xc_cpu_policy_t *guest)
 {
-- 
2.40.0