Introduce a helper to update the CPUID policy using an array of
xen_cpuid_leaf_t entries. Note the leaves present in the input
xen_cpuid_leaf_t array will replace any existing leaves 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:
 - Don't use memcpy.
 - Drop logic to update the leaf manually - x86_cpuid_copy_from_buffer
   already does it.
 - Only print a failure message if err_leaf != -1.
---
 tools/include/xenctrl.h         |  3 +++
 tools/libs/guest/xg_cpuid_x86.c | 20 ++++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/tools/include/xenctrl.h b/tools/include/xenctrl.h
index 605c632cf30..49f919f16a7 100644
--- a/tools/include/xenctrl.h
+++ b/tools/include/xenctrl.h
@@ -2613,6 +2613,9 @@ int xc_cpu_policy_get_cpuid(xc_interface *xch, const xc_cpu_policy_t policy,
                             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_cpu_policy_update_cpuid(xc_interface *xch, xc_cpu_policy_t policy,
+                               const xen_cpuid_leaf_t *leaves,
+                               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 a4307d50ddb..00595e14cc3 100644
--- a/tools/libs/guest/xg_cpuid_x86.c
+++ b/tools/libs/guest/xg_cpuid_x86.c
@@ -887,3 +887,23 @@ int xc_cpu_policy_get_msr(xc_interface *xch, const xc_cpu_policy_t policy,
     *out = *tmp;
     return 0;
 }
+
+int xc_cpu_policy_update_cpuid(xc_interface *xch, xc_cpu_policy_t policy,
+                               const xen_cpuid_leaf_t *leaves,
+                               uint32_t nr)
+{
+    unsigned int err_leaf = -1, err_subleaf = -1;
+    int rc = x86_cpuid_copy_from_buffer(&policy->cpuid, leaves, nr,
+                                        &err_leaf, &err_subleaf);
+
+    if ( rc )
+    {
+        if ( err_leaf != -1 )
+            ERROR("Failed to update CPUID (err leaf %#x, subleaf %#x) (%d = %s)",
+                  err_leaf, err_subleaf, -rc, strerror(-rc));
+        errno = -rc;
+        rc = -1;
+    }
+
+    return rc;
+}
-- 
2.30.1