[PATCH 03/35] hw/intc/arm_gicv3_cpuif: handle LPIs in in the list registers

[Peter Maydell]

The hypervisor can deliver (virtual) LPIs to a guest by setting up a
list register to have an intid which is an LPI.  The GIC has to treat
these a little differently to standard interrupt IDs, because LPIs
have no Active state, and so the guest will only EOI them, it will
not also deactivate them.  So icv_eoir_write() must do two things:

 * if the LPI ID is not in any list register, we drop the
   priority but do not increment the EOI count
 * if the LPI ID is in a list register, we immediately deactivate
   it, regardless of the split-drop-and-deactivate control

This can be seen in the VirtualWriteEOIR0() and VirtualWriteEOIR1()
pseudocode in the GICv3 architecture specification.

Without this fix, potentially a hypervisor guest might stall because
LPIs get stuck in a bogus Active+Pending state.

Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
Weirdly, I only saw this being a problem when the hypervisor guest
was an EL2-enabled one under my FEAT_NV/FEAT_NV2 implementation.
But there's nothing FEAT_NV specific about the bug.
---
 hw/intc/arm_gicv3_cpuif.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/hw/intc/arm_gicv3_cpuif.c b/hw/intc/arm_gicv3_cpuif.c
index ab1a00508e6..258dee1b808 100644
--- a/hw/intc/arm_gicv3_cpuif.c
+++ b/hw/intc/arm_gicv3_cpuif.c
@@ -1434,16 +1434,25 @@ static void icv_eoir_write(CPUARMState *env, const 
ARMCPRegInfo *ri,
     idx = icv_find_active(cs, irq);
 
     if (idx < 0) {
-        /* No valid list register corresponding to EOI ID */
-        icv_increment_eoicount(cs);
+        /*
+         * No valid list register corresponding to EOI ID; if this is a vLPI
+         * not in the list regs then do nothing; otherwise increment EOI count
+         */
+        if (irq < GICV3_LPI_INTID_START) {
+            icv_increment_eoicount(cs);
+        }
     } else {
         uint64_t lr = cs->ich_lr_el2[idx];
         int thisgrp = (lr & ICH_LR_EL2_GROUP) ? GICV3_G1NS : GICV3_G0;
         int lr_gprio = ich_lr_prio(lr) & icv_gprio_mask(cs, grp);
 
         if (thisgrp == grp && lr_gprio == dropprio) {
-            if (!icv_eoi_split(env, cs)) {
-                /* Priority drop and deactivate not split: deactivate irq now 
*/
+            if (!icv_eoi_split(env, cs) || irq >= GICV3_LPI_INTID_START) {
+                /*
+                 * Priority drop and deactivate not split: deactivate irq now.
+                 * LPIs always get their active state cleared immediately
+                 * because no separate deactivate is expected.
+                 */
                 icv_deactivate_irq(cs, idx);
             }
         }
-- 
2.34.1