target/ppc/spapr: Add workaround option to SPAPR_CAP_IBS

The spapr_cap SPAPR_CAP_IBS is used to indicate the level of capability
for mitigations for indirect branch speculation. Currently the available
values are broken (default), fixed-ibs (fixed by serialising indirect
branches) and fixed-ccd (fixed by diabling the count cache).

Introduce a new value for this capability denoted workaround, meaning that
software can work around the issue by flushing the count cache on
context switch. This option is available if the hypervisor sets the
H_CPU_BEHAV_FLUSH_COUNT_CACHE flag in the cpu behaviours returned from
the KVM_PPC_GET_CPU_CHAR ioctl.

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Message-Id: <20190301031912.28809-1-sjitindarsingh@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

2 files changed, 15 insertions, 11 deletions

diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
index faab472d06..ca35b5153d 100644
--- a/hw/ppc/spapr_caps.c
+++ b/hw/ppc/spapr_caps.c
@@ -276,11 +276,13 @@ static void cap_safe_bounds_check_apply(sPAPRMachineState *spapr, uint8_t val,
 }
 
 sPAPRCapPossible cap_ibs_possible = {
-    .num = 4,
+    .num = 5,
     /* Note workaround only maintained for compatibility */
-    .vals = {"broken", "workaround", "fixed-ibs", "fixed-ccd"},
-    .help = "broken - no protection, fixed-ibs - indirect branch serialisation,"
-            " fixed-ccd - cache count disabled",
+    .vals = {"broken", "workaround", "fixed-ibs", "fixed-ccd", "fixed-na"},
+    .help = "broken - no protection, workaround - count cache flush"
+            ", fixed-ibs - indirect branch serialisation,"
+            " fixed-ccd - cache count disabled,"
+            " fixed-na - fixed in hardware (no longer applicable)",
 };
 
 static void cap_safe_indirect_branch_apply(sPAPRMachineState *spapr,
@@ -288,15 +290,11 @@ static void cap_safe_indirect_branch_apply(sPAPRMachineState *spapr,
 {
     uint8_t kvm_val = kvmppc_get_cap_safe_indirect_branch();
 
-    if (val == SPAPR_CAP_WORKAROUND) { /* Can only be Broken or Fixed */
-        error_setg(errp,
-"Requested safe indirect branch capability level \"workaround\" not valid, try cap-ibs=%s",
-                   cap_ibs_possible.vals[kvm_val]);
-    } else if (tcg_enabled() && val) {
+    if (tcg_enabled() && val) {
         /* TODO - for now only allow broken for TCG */
         error_setg(errp,
 "Requested safe indirect branch capability level not supported by tcg, try a different value for cap-ibs");
-    } else if (kvm_enabled() && val && (val != kvm_val)) {
+    } else if (kvm_enabled() && (val > kvm_val)) {
         error_setg(errp,
 "Requested safe indirect branch capability level not supported by kvm, try cap-ibs=%s",
                    cap_ibs_possible.vals[kvm_val]);
@@ -494,7 +492,8 @@ sPAPRCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
     [SPAPR_CAP_IBS] = {
         .name = "ibs",
         .description =
-            "Indirect Branch Speculation (broken, fixed-ibs, fixed-ccd)",
+            "Indirect Branch Speculation (broken, workaround, fixed-ibs,"
+            "fixed-ccd, fixed-na)",
         .index = SPAPR_CAP_IBS,
         .get = spapr_cap_get_string,
         .set = spapr_cap_set_string,
diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
index 476bad6271..4aa8036fc0 100644
--- a/hw/ppc/spapr_hcall.c
+++ b/hw/ppc/spapr_hcall.c
@@ -1723,12 +1723,17 @@ static target_ulong h_get_cpu_characteristics(PowerPCCPU *cpu,
     }
 
     switch (safe_indirect_branch) {
+    case SPAPR_CAP_FIXED_NA:
+        break;
     case SPAPR_CAP_FIXED_CCD:
         characteristics |= H_CPU_CHAR_CACHE_COUNT_DIS;
         break;
     case SPAPR_CAP_FIXED_IBS:
         characteristics |= H_CPU_CHAR_BCCTRL_SERIALISED;
         break;
+    case SPAPR_CAP_WORKAROUND:
+        behaviour |= H_CPU_BEHAV_FLUSH_COUNT_CACHE;
+        break;
     default: /* broken */
         assert(safe_indirect_branch == SPAPR_CAP_BROKEN);
         break;