Introduce a helper to update the MSR policy using an array of
xen_msr_entry_t entries. Note the MSRs present in the input
xen_msr_entry_t array will replace any existing entries on the
policy.

No user of the interface introduced on this patch.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
Changes since v1:
 - Drop logic to update entries manually.
 - Only print failure message if err_msr != -1.
---
 tools/include/xenctrl.h         |  2 ++
 tools/libs/guest/xg_cpuid_x86.c | 18 ++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/tools/include/xenctrl.h b/tools/include/xenctrl.h
index 49f919f16a7..9a6d1b126d8 100644
--- a/tools/include/xenctrl.h
+++ b/tools/include/xenctrl.h
@@ -2616,6 +2616,8 @@ int xc_cpu_policy_get_msr(xc_interface *xch, const xc_cpu_policy_t policy,
 int xc_cpu_policy_update_cpuid(xc_interface *xch, xc_cpu_policy_t policy,
                                const xen_cpuid_leaf_t *leaves,
                                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_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 00595e14cc3..26b09322dfa 100644
--- a/tools/libs/guest/xg_cpuid_x86.c
+++ b/tools/libs/guest/xg_cpuid_x86.c
@@ -907,3 +907,21 @@ int xc_cpu_policy_update_cpuid(xc_interface *xch, xc_cpu_policy_t policy,
 
     return rc;
 }
+
+int xc_cpu_policy_update_msrs(xc_interface *xch, xc_cpu_policy_t policy,
+                              const xen_msr_entry_t *msrs, uint32_t nr)
+{
+    unsigned int err_msr = -1;
+    int rc = x86_msr_copy_from_buffer(&policy->msr, msrs, nr, &err_msr);
+
+    if ( rc )
+    {
+        if ( err_msr != -1 )
+            ERROR("Failed to deserialise MSRS (err index %#x) (%d = %s)",
+                  err_msr, -rc, strerror(-rc));
+        errno = -rc;
+        rc = -1;
+    }
+
+    return rc;
+}
-- 
2.30.1