spapr: Simplify ovec diff

spapr_ovec_diff(ov, old, new) has somewhat complex semantics.  ov is set
to those bits which are in new but not old, and it returns as a boolean
whether or not there are any bits in old but not new.

It turns out that both callers only care about the second, not the first.
This is basically equivalent to a bitmap subset operation, which is easier
to understand and implement.  So replace spapr_ovec_diff() with
spapr_ovec_subset().

Cc: Mike Roth <mdroth@linux.vnet.ibm.com>

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Cedric Le Goater <clg@fr.ibm.com>

3 files changed, 15 insertions, 37 deletions

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 3dedb41d48..f11422fc41 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -1840,8 +1840,6 @@ static bool spapr_ov5_cas_needed(void *opaque)
 {
     SpaprMachineState *spapr = opaque;
     SpaprOptionVector *ov5_mask = spapr_ovec_new();
-    SpaprOptionVector *ov5_legacy = spapr_ovec_new();
-    SpaprOptionVector *ov5_removed = spapr_ovec_new();
     bool cas_needed;
 
     /* Prior to the introduction of SpaprOptionVector, we had two option
@@ -1873,17 +1871,11 @@ static bool spapr_ov5_cas_needed(void *opaque)
     spapr_ovec_set(ov5_mask, OV5_DRCONF_MEMORY);
     spapr_ovec_set(ov5_mask, OV5_DRMEM_V2);
 
-    /* spapr_ovec_diff returns true if bits were removed. we avoid using
-     * the mask itself since in the future it's possible "legacy" bits may be
-     * removed via machine options, which could generate a false positive
-     * that breaks migration.
-     */
-    spapr_ovec_intersect(ov5_legacy, spapr->ov5, ov5_mask);
-    cas_needed = spapr_ovec_diff(ov5_removed, spapr->ov5, ov5_legacy);
+    /* We need extra information if we have any bits outside the mask
+     * defined above */
+    cas_needed = !spapr_ovec_subset(spapr->ov5, ov5_mask);
 
     spapr_ovec_cleanup(ov5_mask);
-    spapr_ovec_cleanup(ov5_legacy);
-    spapr_ovec_cleanup(ov5_removed);
 
     return cas_needed;
 }
diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
index 0f19be794c..f1799b1b70 100644
--- a/hw/ppc/spapr_hcall.c
+++ b/hw/ppc/spapr_hcall.c
@@ -1671,7 +1671,7 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
     target_ulong fdt_bufsize = args[2];
     target_ulong ov_table;
     uint32_t cas_pvr;
-    SpaprOptionVector *ov1_guest, *ov5_guest, *ov5_cas_old, *ov5_updates;
+    SpaprOptionVector *ov1_guest, *ov5_guest, *ov5_cas_old;
     bool guest_radix;
     Error *local_err = NULL;
     bool raw_mode_supported = false;
@@ -1770,9 +1770,7 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
     /* capabilities that have been added since CAS-generated guest reset.
      * if capabilities have since been removed, generate another reset
      */
-    ov5_updates = spapr_ovec_new();
-    spapr->cas_reboot = spapr_ovec_diff(ov5_updates,
-                                        ov5_cas_old, spapr->ov5_cas);
+    spapr->cas_reboot = !spapr_ovec_subset(ov5_cas_old, spapr->ov5_cas);
     spapr_ovec_cleanup(ov5_cas_old);
     /* Now that processing is finished, set the radix/hash bit for the
      * guest if it requested a valid mode; otherwise terminate the boot. */
@@ -1849,8 +1847,6 @@ static target_ulong h_client_architecture_support(PowerPCCPU *cpu,
         spapr->fdt_blob = fdt;
     }
 
-    spapr_ovec_cleanup(ov5_updates);
-
     if (spapr->cas_reboot) {
         qemu_system_reset_request(SHUTDOWN_CAUSE_SUBSYSTEM_RESET);
     }
diff --git a/hw/ppc/spapr_ovec.c b/hw/ppc/spapr_ovec.c
index 811fadf143..0ff6d1aeae 100644
--- a/hw/ppc/spapr_ovec.c
+++ b/hw/ppc/spapr_ovec.c
@@ -76,31 +76,21 @@ void spapr_ovec_intersect(SpaprOptionVector *ov,
     bitmap_and(ov->bitmap, ov1->bitmap, ov2->bitmap, OV_MAXBITS);
 }
 
-/* returns true if options bits were removed, false otherwise */
-bool spapr_ovec_diff(SpaprOptionVector *ov,
-                     SpaprOptionVector *ov_old,
-                     SpaprOptionVector *ov_new)
+/* returns true if ov1 has a subset of bits in ov2 */
+bool spapr_ovec_subset(SpaprOptionVector *ov1, SpaprOptionVector *ov2)
 {
-    unsigned long *change_mask = bitmap_new(OV_MAXBITS);
-    unsigned long *removed_bits = bitmap_new(OV_MAXBITS);
-    bool bits_were_removed = false;
+    unsigned long *tmp = bitmap_new(OV_MAXBITS);
+    bool result;
 
-    g_assert(ov);
-    g_assert(ov_old);
-    g_assert(ov_new);
-
-    bitmap_xor(change_mask, ov_old->bitmap, ov_new->bitmap, OV_MAXBITS);
-    bitmap_and(ov->bitmap, ov_new->bitmap, change_mask, OV_MAXBITS);
-    bitmap_and(removed_bits, ov_old->bitmap, change_mask, OV_MAXBITS);
+    g_assert(ov1);
+    g_assert(ov2);
 
-    if (!bitmap_empty(removed_bits, OV_MAXBITS)) {
-        bits_were_removed = true;
-    }
+    bitmap_andnot(tmp, ov1->bitmap, ov2->bitmap, OV_MAXBITS);
+    result = bitmap_empty(tmp, OV_MAXBITS);
 
-    g_free(change_mask);
-    g_free(removed_bits);
+    g_free(tmp);
 
-    return bits_were_removed;
+    return result;
 }
 
 void spapr_ovec_cleanup(SpaprOptionVector *ov)