[PATCH v2 6/6] spapr/xive: Introduce a new CAS value for the StoreEOI capability

[Cédric Le Goater]

When the StoreEOI capability is set to "cas", let CAS decide when
StoreEOI should be advertised. StoreEOI is safe to use with a P10
compat machine because the OS enforces load-after-store ordering but
not with P9 compat.

The question now is : should we make "cas" the default at the machine
level ?

Signed-off-by: Cédric Le Goater <clg@kaod.org>
---
 include/hw/ppc/spapr.h      |  1 +
 include/hw/ppc/spapr_xive.h |  1 +
 hw/intc/spapr_xive.c        |  9 +++++++++
 hw/ppc/spapr_caps.c         | 21 +++++++++++++++++----
 hw/ppc/spapr_hcall.c        |  7 +++++++
 5 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
index b701c14b4e09..17e7d873e8dc 100644
--- a/include/hw/ppc/spapr.h
+++ b/include/hw/ppc/spapr.h
@@ -87,6 +87,7 @@ typedef enum {
 #define SPAPR_CAP_ON                    0x01
 
 /* Custom Caps */
+#define SPAPR_CAP_CAS                   0x02
 
 /* Generic */
 #define SPAPR_CAP_BROKEN                0x00
diff --git a/include/hw/ppc/spapr_xive.h b/include/hw/ppc/spapr_xive.h
index 26c8d90d7196..8b8aa586e44f 100644
--- a/include/hw/ppc/spapr_xive.h
+++ b/include/hw/ppc/spapr_xive.h
@@ -75,6 +75,7 @@ void spapr_xive_map_mmio(SpaprXive *xive);
 
 int spapr_xive_end_to_target(uint8_t end_blk, uint32_t end_idx,
                              uint32_t *out_server, uint8_t *out_prio);
+void spapr_xive_enable_store_eoi(SpaprXive *xive, bool enable);
 
 /*
  * KVM XIVE device helpers
diff --git a/hw/intc/spapr_xive.c b/hw/intc/spapr_xive.c
index 41f2719ff93a..f57a2681dd91 100644
--- a/hw/intc/spapr_xive.c
+++ b/hw/intc/spapr_xive.c
@@ -1802,3 +1802,12 @@ void spapr_xive_hcall_init(SpaprMachineState *spapr)
     spapr_register_hypercall(H_INT_SYNC, h_int_sync);
     spapr_register_hypercall(H_INT_RESET, h_int_reset);
 }
+
+void spapr_xive_enable_store_eoi(SpaprXive *xive, bool enable)
+{
+    if (enable) {
+        xive->source.esb_flags |= XIVE_SRC_STORE_EOI;
+    } else {
+        xive->source.esb_flags &= ~XIVE_SRC_STORE_EOI;
+    }
+}
diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
index 9251badbdc27..c55e1fccb9bc 100644
--- a/hw/ppc/spapr_caps.c
+++ b/hw/ppc/spapr_caps.c
@@ -524,6 +524,13 @@ static void cap_fwnmi_apply(SpaprMachineState *spapr, 
uint8_t val,
     }
 }
 
+SpaprCapPossible cap_storeeoi_possible = {
+    .num = 3,
+    .vals = { "off", "on", "cas" },
+    .help = "off - no StoreEOI, on - StoreEOI, "
+            "cas - negotiated at CAS (POWER10 compat only)",
+};
+
 static void cap_storeeoi_apply(SpaprMachineState *spapr, uint8_t val,
                                Error **errp)
 {
@@ -550,6 +557,11 @@ static void cap_storeeoi_apply(SpaprMachineState *spapr, 
uint8_t val,
             return;
         }
 
+        /* CAS will decide to advertise StoreEOI (P10 compat kernels only) */
+        if (val == SPAPR_CAP_CAS) {
+            return;
+        }
+
         /*
          * load-after-store ordering is not enforced on POWER9 CPUs
          * and StoreEOI can be racy.
@@ -671,11 +683,12 @@ SpaprCapabilityInfo capability_table[SPAPR_CAP_NUM] = {
     },
     [SPAPR_CAP_STOREEOI] = {
         .name = "storeeoi",
-        .description = "Implements XIVE StoreEOI feature",
+        .description = "Implements XIVE StoreEOI feature (off, on, cas)",
         .index = SPAPR_CAP_STOREEOI,
-        .get = spapr_cap_get_bool,
-        .set = spapr_cap_set_bool,
-        .type = "bool",
+        .get = spapr_cap_get_string,
+        .set = spapr_cap_set_string,
+        .type = "string",
+        .possible = &cap_storeeoi_possible,
         .apply = cap_storeeoi_apply,
     },
 };
diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
index 607740150fa2..158b122b9192 100644
--- a/hw/ppc/spapr_hcall.c
+++ b/hw/ppc/spapr_hcall.c
@@ -1804,6 +1804,13 @@ target_ulong do_client_architecture_support(PowerPCCPU 
*cpu,
 "Guest requested unavailable interrupt mode (XIVE), try the ic-mode=xive or 
ic-mode=dual machine property");
             exit(EXIT_FAILURE);
         }
+
+        /* Advertise StoreEOI for a P10 compat guest. */
+        if (spapr_get_cap(spapr, SPAPR_CAP_STOREEOI) == SPAPR_CAP_CAS) {
+            bool enable = ppc_check_compat(cpu, CPU_POWERPC_LOGICAL_3_10, 0,
+                                           cpu->compat_pvr);
+            spapr_xive_enable_store_eoi(spapr->xive, enable);
+        }
     } else {
         if (!spapr->irq->xics) {
             error_report(
-- 
2.25.4