ppc/xive2: Support group-matching when looking for target

If an END has the 'i' bit set (ignore), then it targets a group of
VPs. The size of the group depends on the VP index of the target
(first 0 found when looking at the least significant bits of the
index) so a mask is applied on the VP index of a running thread to
know if we have a match.

Signed-off-by: Frederic Barrat <fbarrat@linux.ibm.com>
Signed-off-by: Michael Kowal <kowal@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

hw/intc/pnv_xive2.c

@@ -1,10 +1,9 @@
 /*
  * QEMU PowerPC XIVE2 interrupt controller model  (POWER10)
  *
- * Copyright (c) 2019-2022, IBM Corporation.
+ * Copyright (c) 2019-2024, IBM Corporation.
  *
- * This code is licensed under the GPL version 2 or later. See the
+ * SPDX-License-Identifier: GPL-2.0-or-later
- * COPYING file in the top-level directory.
  */
 
 #include "qemu/osdep.h"
@@ -660,24 +659,37 @@ static int pnv_xive2_match_nvt(XivePresenter *xptr, uint8_t format,
                                                    logic_serv);
             }
 
-            /*
-             * Save the context and follow on to catch duplicates,
-             * that we don't support yet.
-             */
             if (ring != -1) {
-                if (match->tctx) {
+                /*
+                 * For VP-specific match, finding more than one is a
+                 * problem. For group notification, it's possible.
+                 */
+                if (!cam_ignore && match->tctx) {
                     qemu_log_mask(LOG_GUEST_ERROR, "XIVE: already found a "
                                   "thread context NVT %x/%x\n",
                                   nvt_blk, nvt_idx);
-                    return false;
+                    /* Should set a FIR if we ever model it */
+                    return -1;
                 }
-
+                /*
+                 * For a group notification, we need to know if the
+                 * match is precluded first by checking the current
+                 * thread priority. If the interrupt can be delivered,
+                 * we always notify the first match (for now).
+                 */
+                if (cam_ignore &&
+                    xive2_tm_irq_precluded(tctx, ring, priority)) {
+                        match->precluded = true;
+                } else {
+                    if (!match->tctx) {
                         match->ring = ring;
                         match->tctx = tctx;
+                    }
                     count++;
                 }
             }
         }
+    }
 
     return count;
 }

hw/intc/xive.c

@@ -1655,6 +1655,16 @@ static uint32_t xive_tctx_hw_cam_line(XivePresenter *xptr, XiveTCTX *tctx)
     return xive_nvt_cam_line(blk, 1 << 7 | (pir & 0x7f));
 }
 
+uint32_t xive_get_vpgroup_size(uint32_t nvp_index)
+{
+    /*
+     * Group size is a power of 2. The position of the first 0
+     * (starting with the least significant bits) in the NVP index
+     * gives the size of the group.
+     */
+    return 1 << (ctz32(~nvp_index) + 1);
+}
+
 static uint8_t xive_get_group_level(uint32_t nvp_index)
 {
     /* FIXME add crowd encoding */
@@ -1727,30 +1737,39 @@ int xive_presenter_tctx_match(XivePresenter *xptr, XiveTCTX *tctx,
 /*
  * This is our simple Xive Presenter Engine model. It is merged in the
  * Router as it does not require an extra object.
- *
- * It receives notification requests sent by the IVRE to find one
- * matching NVT (or more) dispatched on the processor threads. In case
- * of a single NVT notification, the process is abbreviated and the
- * thread is signaled if a match is found. In case of a logical server
- * notification (bits ignored at the end of the NVT identifier), the
- * IVPE and IVRE select a winning thread using different filters. This
- * involves 2 or 3 exchanges on the PowerBus that the model does not
- * support.
- *
- * The parameters represent what is sent on the PowerBus
  */
 bool xive_presenter_notify(XiveFabric *xfb, uint8_t format,
                            uint8_t nvt_blk, uint32_t nvt_idx,
                            bool cam_ignore, uint8_t priority,
-                           uint32_t logic_serv)
+                           uint32_t logic_serv, bool *precluded)
 {
     XiveFabricClass *xfc = XIVE_FABRIC_GET_CLASS(xfb);
-    XiveTCTXMatch match = { .tctx = NULL, .ring = 0 };
+    XiveTCTXMatch match = { .tctx = NULL, .ring = 0, .precluded = false };
     uint8_t group_level;
     int count;
 
     /*
-     * Ask the machine to scan the interrupt controllers for a match
+     * Ask the machine to scan the interrupt controllers for a match.
+     *
+     * For VP-specific notification, we expect at most one match and
+     * one call to the presenters is all we need (abbreviated notify
+     * sequence documented by the architecture).
+     *
+     * For VP-group notification, match_nvt() is the equivalent of the
+     * "histogram" and "poll" commands sent to the power bus to the
+     * presenters. 'count' could be more than one, but we always
+     * select the first match for now. 'precluded' tells if (at least)
+     * one thread matches but can't take the interrupt now because
+     * it's running at a more favored priority. We return the
+     * information to the router so that it can take appropriate
+     * actions (backlog, escalation, broadcast, etc...)
+     *
+     * If we were to implement a better way of dispatching the
+     * interrupt in case of multiple matches (instead of the first
+     * match), we would need a heuristic to elect a thread (for
+     * example, the hardware keeps track of an 'age' in the TIMA) and
+     * a new command to the presenters (the equivalent of the "assign"
+     * power bus command in the documented full notify sequence.
      */
     count = xfc->match_nvt(xfb, format, nvt_blk, nvt_idx, cam_ignore,
                            priority, logic_serv, &match);
@@ -1763,6 +1782,8 @@ bool xive_presenter_notify(XiveFabric *xfb, uint8_t format,
         group_level = cam_ignore ? xive_get_group_level(nvt_idx) : 0;
         trace_xive_presenter_notify(nvt_blk, nvt_idx, match.ring, group_level);
         xive_tctx_pipr_update(match.tctx, match.ring, priority, group_level);
+    } else {
+        *precluded = match.precluded;
     }
 
     return !!count;
@@ -1802,7 +1823,7 @@ void xive_router_end_notify(XiveRouter *xrtr, XiveEAS *eas)
     uint8_t nvt_blk;
     uint32_t nvt_idx;
     XiveNVT nvt;
-    bool found;
+    bool found, precluded;
 
     uint8_t end_blk = xive_get_field64(EAS_END_BLOCK, eas->w);
     uint32_t end_idx = xive_get_field64(EAS_END_INDEX, eas->w);
@@ -1885,8 +1906,9 @@ void xive_router_end_notify(XiveRouter *xrtr, XiveEAS *eas)
     found = xive_presenter_notify(xrtr->xfb, format, nvt_blk, nvt_idx,
                           xive_get_field32(END_W7_F0_IGNORE, end.w7),
                           priority,
-                          xive_get_field32(END_W7_F1_LOG_SERVER_ID, end.w7));
+                          xive_get_field32(END_W7_F1_LOG_SERVER_ID, end.w7),
-
+                          &precluded);
+    /* we don't support VP-group notification on P9, so precluded is not used */
     /* TODO: Auto EOI. */
 
     if (found) {

hw/intc/xive2.c

@@ -739,6 +739,12 @@ int xive2_router_write_nvgc(Xive2Router *xrtr, bool crowd,
    return xrc->write_nvgc(xrtr, crowd, nvgc_blk, nvgc_idx, nvgc);
 }
 
+static bool xive2_vp_match_mask(uint32_t cam1, uint32_t cam2,
+                                uint32_t vp_mask)
+{
+    return (cam1 & vp_mask) == (cam2 & vp_mask);
+}
+
 /*
  * The thread context register words are in big-endian format.
  */
@@ -753,44 +759,50 @@ int xive2_presenter_tctx_match(XivePresenter *xptr, XiveTCTX *tctx,
     uint32_t qw1w2 = xive_tctx_word2(&tctx->regs[TM_QW1_OS]);
     uint32_t qw0w2 = xive_tctx_word2(&tctx->regs[TM_QW0_USER]);
 
-    /*
+    uint32_t vp_mask = 0xFFFFFFFF;
-     * TODO (PowerNV): ignore mode. The low order bits of the NVT
-     * identifier are ignored in the "CAM" match.
-     */
 
     if (format == 0) {
-        if (cam_ignore == true) {
         /*
-             * F=0 & i=1: Logical server notification (bits ignored at
+         * i=0: Specific NVT notification
-             * the end of the NVT identifier)
+         * i=1: VP-group notification (bits ignored at the end of the
+         *      NVT identifier)
          */
-            qemu_log_mask(LOG_UNIMP, "XIVE: no support for LS NVT %x/%x\n",
+        if (cam_ignore) {
-                          nvt_blk, nvt_idx);
+            vp_mask = ~(xive_get_vpgroup_size(nvt_idx) - 1);
-            return -1;
         }
 
-        /* F=0 & i=0: Specific NVT notification */
+        /* For VP-group notifications, threads with LGS=0 are excluded */
 
         /* PHYS ring */
         if ((be32_to_cpu(qw3w2) & TM2_QW3W2_VT) &&
-            cam == xive2_tctx_hw_cam_line(xptr, tctx)) {
+            !(cam_ignore && tctx->regs[TM_QW3_HV_PHYS + TM_LGS] == 0) &&
+            xive2_vp_match_mask(cam,
+                                xive2_tctx_hw_cam_line(xptr, tctx),
+                                vp_mask)) {
             return TM_QW3_HV_PHYS;
         }
 
         /* HV POOL ring */
         if ((be32_to_cpu(qw2w2) & TM2_QW2W2_VP) &&
-            cam == xive_get_field32(TM2_QW2W2_POOL_CAM, qw2w2)) {
+            !(cam_ignore && tctx->regs[TM_QW2_HV_POOL + TM_LGS] == 0) &&
+            xive2_vp_match_mask(cam,
+                                xive_get_field32(TM2_QW2W2_POOL_CAM, qw2w2),
+                                vp_mask)) {
             return TM_QW2_HV_POOL;
         }
 
         /* OS ring */
         if ((be32_to_cpu(qw1w2) & TM2_QW1W2_VO) &&
-            cam == xive_get_field32(TM2_QW1W2_OS_CAM, qw1w2)) {
+            !(cam_ignore && tctx->regs[TM_QW1_OS + TM_LGS] == 0) &&
+            xive2_vp_match_mask(cam,
+                                xive_get_field32(TM2_QW1W2_OS_CAM, qw1w2),
+                                vp_mask)) {
             return TM_QW1_OS;
         }
     } else {
         /* F=1 : User level Event-Based Branch (EBB) notification */
 
+        /* FIXME: what if cam_ignore and LGS = 0 ? */
         /* USER ring */
         if  ((be32_to_cpu(qw1w2) & TM2_QW1W2_VO) &&
              (cam == xive_get_field32(TM2_QW1W2_OS_CAM, qw1w2)) &&
@@ -802,6 +814,22 @@ int xive2_presenter_tctx_match(XivePresenter *xptr, XiveTCTX *tctx,
     return -1;
 }
 
+bool xive2_tm_irq_precluded(XiveTCTX *tctx, int ring, uint8_t priority)
+{
+    uint8_t *regs = &tctx->regs[ring];
+
+    /*
+     * The xive2_presenter_tctx_match() above tells if there's a match
+     * but for VP-group notification, we still need to look at the
+     * priority to know if the thread can take the interrupt now or if
+     * it is precluded.
+     */
+    if (priority < regs[TM_CPPR]) {
+        return false;
+    }
+    return true;
+}
+
 static void xive2_router_realize(DeviceState *dev, Error **errp)
 {
     Xive2Router *xrtr = XIVE2_ROUTER(dev);
@@ -841,7 +869,7 @@ static void xive2_router_end_notify(Xive2Router *xrtr, uint8_t end_blk,
     Xive2End end;
     uint8_t priority;
     uint8_t format;
-    bool found;
+    bool found, precluded;
     Xive2Nvp nvp;
     uint8_t nvp_blk;
     uint32_t nvp_idx;
@@ -922,7 +950,8 @@ static void xive2_router_end_notify(Xive2Router *xrtr, uint8_t end_blk,
     found = xive_presenter_notify(xrtr->xfb, format, nvp_blk, nvp_idx,
                           xive2_end_is_ignore(&end),
                           priority,
-                          xive_get_field32(END2_W7_F1_LOG_SERVER_ID, end.w7));
+                          xive_get_field32(END2_W7_F1_LOG_SERVER_ID, end.w7),
+                          &precluded);
 
     /* TODO: Auto EOI. */
 

include/hw/ppc/xive.h

@@ -422,6 +422,7 @@ void xive_router_end_notify(XiveRouter *xrtr, XiveEAS *eas);
 typedef struct XiveTCTXMatch {
     XiveTCTX *tctx;
     uint8_t ring;
+    bool precluded;
 } XiveTCTXMatch;
 
 #define TYPE_XIVE_PRESENTER "xive-presenter"
@@ -450,7 +451,9 @@ int xive_presenter_tctx_match(XivePresenter *xptr, XiveTCTX *tctx,
 bool xive_presenter_notify(XiveFabric *xfb, uint8_t format,
                            uint8_t nvt_blk, uint32_t nvt_idx,
                            bool cam_ignore, uint8_t priority,
-                           uint32_t logic_serv);
+                           uint32_t logic_serv, bool *precluded);
+
+uint32_t xive_get_vpgroup_size(uint32_t nvp_index);
 
 /*
  * XIVE Fabric (Interface between Interrupt Controller and Machine)

include/hw/ppc/xive2.h

@@ -1,11 +1,9 @@
 /*
  * QEMU PowerPC XIVE2 interrupt controller model  (POWER10)
  *
- * Copyright (c) 2019-2022, IBM Corporation.
+ * Copyright (c) 2019-2024, IBM Corporation.
- *
- * This code is licensed under the GPL version 2 or later. See the
- * COPYING file in the top-level directory.
  *
+ * SPDX-License-Identifier: GPL-2.0-or-later
  */
 
 #ifndef PPC_XIVE2_H
@@ -121,6 +119,7 @@ uint64_t xive2_tm_pull_os_ctx(XivePresenter *xptr, XiveTCTX *tctx,
                                hwaddr offset, unsigned size);
 void xive2_tm_pull_os_ctx_ol(XivePresenter *xptr, XiveTCTX *tctx,
                              hwaddr offset, uint64_t value, unsigned size);
+bool xive2_tm_irq_precluded(XiveTCTX *tctx, int ring, uint8_t priority);
 void xive2_tm_set_hv_target(XivePresenter *xptr, XiveTCTX *tctx,
                             hwaddr offset, uint64_t value, unsigned size);
 void xive2_tm_pull_phys_ctx_ol(XivePresenter *xptr, XiveTCTX *tctx,