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@citrix.com>
---
Changes since v3:
 - Use x86_msr_get_entry.

Changes since v1:
 - Introduce a helper to perform a binary search of the MSR entries
   array.
---
 tools/include/xenguest.h        |  2 ++
 tools/libs/guest/xg_cpuid_x86.c | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/tools/include/xenguest.h b/tools/include/xenguest.h
index 7001e04e88d..8e8461b0660 100644
--- a/tools/include/xenguest.h
+++ b/tools/include/xenguest.h
@@ -747,6 +747,8 @@ int xc_cpu_policy_update_msrs(xc_interface *xch, 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);
 
 /* 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 460512d063b..cdfc79a86e7 100644
--- a/tools/libs/guest/xg_cpuid_x86.c
+++ b/tools/libs/guest/xg_cpuid_x86.c
@@ -883,6 +883,26 @@ int xc_cpu_policy_get_cpuid(xc_interface *xch, const xc_cpu_policy_t *policy,
     return 0;
 }
 
+int xc_cpu_policy_get_msr(xc_interface *xch, const xc_cpu_policy_t *policy,
+                          uint32_t msr, xen_msr_entry_t *out)
+{
+    const uint64_t *val;
+
+    *out = (xen_msr_entry_t){};
+
+    val = x86_msr_get_entry(&policy->msr, msr);
+    if ( !val )
+    {
+        errno = ENOENT;
+        return -1;
+    }
+
+    out->idx = msr;
+    out->val = *val;
+
+    return 0;
+}
+
 bool xc_cpu_policy_is_compatible(xc_interface *xch, xc_cpu_policy_t *host,
                                  xc_cpu_policy_t *guest)
 {
-- 
2.31.1