From 7693449b235bbab6d32a1b87fa1d0e101c786f3b Mon Sep 17 00:00:00 2001
From: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Date: Thu, 9 Mar 2023 08:11:14 -0500
Subject: [PATCH 05/13] edu: add smp_mb__after_rmw()

RH-Author: Emanuele Giuseppe Esposito <eesposit@redhat.com>
RH-MergeRequest: 263: qatomic: add smp_mb__before/after_rmw()
RH-Bugzilla: 2168472
RH-Acked-by: Cornelia Huck <cohuck@redhat.com>
RH-Acked-by: Eric Auger <eric.auger@redhat.com>
RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
RH-Acked-by: David Hildenbrand <david@redhat.com>
RH-Commit: [5/10] 300901290e08b253b1278eedc39cd07c1e202b96

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2168472

commit 2482aeea4195ad84cf3d4e5b15b28ec5b420ed5a
Author: Paolo Bonzini <pbonzini@redhat.com>
Date:   Thu Mar 2 11:16:13 2023 +0100

    edu: add smp_mb__after_rmw()

    Ensure ordering between clearing the COMPUTING flag and checking
    IRQFACT, and between setting the IRQFACT flag and checking
    COMPUTING.  This ensures that no wakeups are lost.

    Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
    Reviewed-by: David Hildenbrand <david@redhat.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 hw/misc/edu.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/hw/misc/edu.c b/hw/misc/edu.c
index e935c418d4..a1f8bc77e7 100644
--- a/hw/misc/edu.c
+++ b/hw/misc/edu.c
@@ -267,6 +267,8 @@ static void edu_mmio_write(void *opaque, hwaddr addr, uint64_t val,
     case 0x20:
         if (val & EDU_STATUS_IRQFACT) {
             qatomic_or(&edu->status, EDU_STATUS_IRQFACT);
+            /* Order check of the COMPUTING flag after setting IRQFACT.  */
+            smp_mb__after_rmw();
         } else {
             qatomic_and(&edu->status, ~EDU_STATUS_IRQFACT);
         }
@@ -349,6 +351,9 @@ static void *edu_fact_thread(void *opaque)
         qemu_mutex_unlock(&edu->thr_mutex);
         qatomic_and(&edu->status, ~EDU_STATUS_COMPUTING);
 
+        /* Clear COMPUTING flag before checking IRQFACT.  */
+        smp_mb__after_rmw();
+
         if (qatomic_read(&edu->status) & EDU_STATUS_IRQFACT) {
             qemu_mutex_lock_iothread();
             edu_raise_irq(edu, FACT_IRQ);
-- 
2.37.3