[PATCH 12/21] libs/guest: allow updating a cpu policy MSR data

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

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@xxxxxxxxxx>
---
 tools/include/xenctrl.h         |  2 +
 tools/libs/guest/xg_cpuid_x86.c | 65 +++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+)

diff --git a/tools/include/xenctrl.h b/tools/include/xenctrl.h
index 2143478fe4b..46f5026081c 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 13c2972ccd3..07756743e76 100644
--- a/tools/libs/guest/xg_cpuid_x86.c
+++ b/tools/libs/guest/xg_cpuid_x86.c
@@ -1033,3 +1033,68 @@ int xc_cpu_policy_update_cpuid(xc_interface *xch, 
xc_cpu_policy_t policy,
     free(current);
     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;
+    unsigned int nr_leaves, nr_msrs, i, j;
+    xen_msr_entry_t *current;
+    int rc = xc_cpu_policy_get_size(xch, &nr_leaves, &nr_msrs);
+
+    if ( rc )
+    {
+        PERROR("Failed to obtain policy info size");
+        return -1;
+    }
+
+    current = calloc(nr_msrs, sizeof(*current));
+    if ( !current )
+    {
+        PERROR("Failed to allocate resources");
+        errno = ENOMEM;
+        return -1;
+    }
+
+    rc = xc_cpu_policy_serialise(xch, policy, NULL, 0, current, &nr_msrs);
+    if ( rc )
+        goto out;
+
+    for ( i = 0; i < nr; i++ )
+    {
+        const xen_msr_entry_t *update = &msrs[i];
+
+        for ( j = 0; j < nr_msrs; j++ )
+            if ( current[j].idx == update->idx )
+            {
+                /*
+                 * NB: cannot use an assignation because of the const vs
+                 * non-const difference.
+                 */
+                memcpy(&current[j], update, sizeof(*update));
+                break;
+            }
+
+        if ( j == nr_msrs )
+        {
+            /* Failed to find a matching MSR, append to the end. */
+            current = realloc(current, (nr_msrs + 1) * sizeof(*current));
+            memcpy(&current[nr_msrs], update, sizeof(*update));
+            nr_msrs++;
+        }
+    }
+
+    rc = x86_msr_copy_from_buffer(policy->msr, current, nr_msrs, &err_msr);
+    if ( rc )
+    {
+        ERROR("Failed to deserialise MSRS (err index %#x) (%d = %s)",
+              err_msr, -rc, strerror(-rc));
+        errno = -rc;
+        rc = -1;
+    }
+
+ out:
+    free(current);
+    return rc;
+
+}
-- 
2.30.1