[PATCH 10/21] libs/guest: allow fetching a specific MSR entry from a cpu policy

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

Introduce an interface that returns a specific MSR entry from a cpu
policy in xen_msr_entry_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>
---
 tools/include/xenctrl.h         |  2 ++
 tools/libs/guest/xg_cpuid_x86.c | 41 +++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/tools/include/xenctrl.h b/tools/include/xenctrl.h
index 983e4c11d93..ab34df1dc98 100644
--- a/tools/include/xenctrl.h
+++ b/tools/include/xenctrl.h
@@ -2611,6 +2611,8 @@ int xc_cpu_policy_serialise(xc_interface *xch, const 
xc_cpu_policy_t policy,
 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);
+int xc_cpu_policy_get_msr(xc_interface *xch, const xc_cpu_policy_t policy,
+                          uint32_t msr, xen_msr_entry_t *out);
 
 int xc_get_cpu_levelling_caps(xc_interface *xch, uint32_t *caps);
 int xc_get_cpu_featureset(xc_interface *xch, uint32_t index,
diff --git a/tools/libs/guest/xg_cpuid_x86.c b/tools/libs/guest/xg_cpuid_x86.c
index a1e1bf10d5c..091aeb70c9c 100644
--- a/tools/libs/guest/xg_cpuid_x86.c
+++ b/tools/libs/guest/xg_cpuid_x86.c
@@ -925,3 +925,44 @@ int xc_cpu_policy_get_cpuid(xc_interface *xch, const 
xc_cpu_policy_t policy,
     free(leaves);
     return rc;
 }
+
+int xc_cpu_policy_get_msr(xc_interface *xch, const xc_cpu_policy_t policy,
+                          uint32_t msr, xen_msr_entry_t *out)
+{
+    unsigned int nr_leaves, nr_msrs, i;
+    xen_msr_entry_t *msrs;
+    int rc = xc_cpu_policy_get_size(xch, &nr_leaves, &nr_msrs);
+
+    if ( rc )
+    {
+        PERROR("Failed to obtain policy info size");
+        return -1;
+    }
+
+    msrs = calloc(nr_msrs, sizeof(*msrs));
+    if ( !msrs )
+    {
+        PERROR("Failed to allocate resources");
+        errno = ENOMEM;
+        return -1;
+    }
+
+    rc = xc_cpu_policy_serialise(xch, policy, NULL, 0, msrs, &nr_msrs);
+    if ( rc )
+        goto out;
+
+    for ( i = 0; i < nr_msrs; i++ )
+        if ( msrs[i].idx == msr )
+        {
+            *out = msrs[i];
+            goto out;
+        }
+
+    /* Unable to find a matching MSR. */
+    errno = ENOENT;
+    rc = -1;
+
+ out:
+    free(msrs);
+    return rc;
+}
-- 
2.30.1