Commit [1] made qemu fail with abort:
  xen_evtchn_set_gsi: Assertion `bql_locked()' failed.
when running ./tests/functional/x86_64/test_kvm_xen.py tests.

To fix it make sure that BQL is held when manipulating IRQs.

1)
Fixes: 7defb58baf (hpet: switch to fine-grained device locking)
Reported-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
 hw/timer/hpet.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/hw/timer/hpet.c b/hw/timer/hpet.c
index 789a31d0a0..1acba4fa9d 100644
--- a/hw/timer/hpet.c
+++ b/hw/timer/hpet.c
@@ -40,6 +40,7 @@
 #include "qom/object.h"
 #include "qemu/lockable.h"
 #include "qemu/seqlock.h"
+#include "qemu/main-loop.h"
 #include "trace.h"
 
 struct hpet_fw_config hpet_fw_cfg = {.count = UINT8_MAX};
@@ -222,12 +223,15 @@ static void update_irq(struct HPETTimer *timer, int set)
                                  timer->fsb & 0xffffffff, MEMTXATTRS_UNSPECIFIED,
                                  NULL);
         } else if (timer->config & HPET_TN_TYPE_LEVEL) {
+            BQL_LOCK_GUARD();
             qemu_irq_raise(s->irqs[route]);
         } else {
+            BQL_LOCK_GUARD();
             qemu_irq_pulse(s->irqs[route]);
         }
     } else {
         if (!timer_fsb_route(timer)) {
+            BQL_LOCK_GUARD();
             qemu_irq_lower(s->irqs[route]);
         }
     }
@@ -534,10 +538,12 @@ static void hpet_ram_write(void *opaque, hwaddr addr,
             /* i8254 and RTC output pins are disabled
              * when HPET is in legacy mode */
             if (activating_bit(old_val, new_val, HPET_CFG_LEGACY)) {
+                BQL_LOCK_GUARD();
                 qemu_set_irq(s->pit_enabled, 0);
                 qemu_irq_lower(s->irqs[0]);
                 qemu_irq_lower(s->irqs[RTC_ISA_IRQ]);
             } else if (deactivating_bit(old_val, new_val, HPET_CFG_LEGACY)) {
+                BQL_LOCK_GUARD();
                 qemu_irq_lower(s->irqs[0]);
                 qemu_set_irq(s->pit_enabled, 1);
                 qemu_set_irq(s->irqs[RTC_ISA_IRQ], s->rtc_irq_level);
@@ -683,11 +689,13 @@ static void hpet_handle_legacy_irq(void *opaque, int n, int level)
 
     if (n == HPET_LEGACY_PIT_INT) {
         if (!hpet_in_legacy_mode(s)) {
+            BQL_LOCK_GUARD();
             qemu_set_irq(s->irqs[0], level);
         }
     } else {
         s->rtc_irq_level = level;
         if (!hpet_in_legacy_mode(s)) {
+            BQL_LOCK_GUARD();
             qemu_set_irq(s->irqs[RTC_ISA_IRQ], level);
         }
     }
-- 
2.47.3

On 9/10/25 16:25, Igor Mammedov wrote:
> Commit [1] made qemu fail with abort:
>    xen_evtchn_set_gsi: Assertion `bql_locked()' failed.
> when running ./tests/functional/x86_64/test_kvm_xen.py tests.
> 
> To fix it make sure that BQL is held when manipulating IRQs.

Queued, but I think it's time to allow qemu_irq handlers to run outside 
the BQL.

The idea would be to add qemu_allocate_irq_unlocked and 
qemu_allocate_irqs_unlocked, and add a boolean to IRQState.  If the 
boolean is set (the default), qemu_set_irq would wrap the callback with 
bql_lock()/bql_unlock().

Together with the MMIO support that you introduced, this would allow 
making interrupt controllers BQL-free.

Easier thread-safety would also, but I digress, provide a good reason to 
write even the simple devices in Rust---that's in my opinion an even 
better reason than memory safety, for which we already have developed 
lots of abstractions in QEMU.

Paolo

> Fixes: 7defb58baf (hpet: switch to fine-grained device locking)
> Reported-by: Daniel P. Berrangé <berrange@redhat.com>
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
>   hw/timer/hpet.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/hw/timer/hpet.c b/hw/timer/hpet.c
> index 789a31d0a0..1acba4fa9d 100644
> --- a/hw/timer/hpet.c
> +++ b/hw/timer/hpet.c
> @@ -40,6 +40,7 @@
>   #include "qom/object.h"
>   #include "qemu/lockable.h"
>   #include "qemu/seqlock.h"
> +#include "qemu/main-loop.h"
>   #include "trace.h"
>   
>   struct hpet_fw_config hpet_fw_cfg = {.count = UINT8_MAX};
> @@ -222,12 +223,15 @@ static void update_irq(struct HPETTimer *timer, int set)
>                                    timer->fsb & 0xffffffff, MEMTXATTRS_UNSPECIFIED,
>                                    NULL);
>           } else if (timer->config & HPET_TN_TYPE_LEVEL) {
> +            BQL_LOCK_GUARD();
>               qemu_irq_raise(s->irqs[route]);
>           } else {
> +            BQL_LOCK_GUARD();
>               qemu_irq_pulse(s->irqs[route]);
>           }
>       } else {
>           if (!timer_fsb_route(timer)) {
> +            BQL_LOCK_GUARD();
>               qemu_irq_lower(s->irqs[route]);
>           }
>       }
> @@ -534,10 +538,12 @@ static void hpet_ram_write(void *opaque, hwaddr addr,
>               /* i8254 and RTC output pins are disabled
>                * when HPET is in legacy mode */
>               if (activating_bit(old_val, new_val, HPET_CFG_LEGACY)) {
> +                BQL_LOCK_GUARD();
>                   qemu_set_irq(s->pit_enabled, 0);
>                   qemu_irq_lower(s->irqs[0]);
>                   qemu_irq_lower(s->irqs[RTC_ISA_IRQ]);
>               } else if (deactivating_bit(old_val, new_val, HPET_CFG_LEGACY)) {
> +                BQL_LOCK_GUARD();
>                   qemu_irq_lower(s->irqs[0]);
>                   qemu_set_irq(s->pit_enabled, 1);
>                   qemu_set_irq(s->irqs[RTC_ISA_IRQ], s->rtc_irq_level);
> @@ -683,11 +689,13 @@ static void hpet_handle_legacy_irq(void *opaque, int n, int level)
>   
>       if (n == HPET_LEGACY_PIT_INT) {
>           if (!hpet_in_legacy_mode(s)) {
> +            BQL_LOCK_GUARD();
>               qemu_set_irq(s->irqs[0], level);
>           }
>       } else {
>           s->rtc_irq_level = level;
>           if (!hpet_in_legacy_mode(s)) {
> +            BQL_LOCK_GUARD();
>               qemu_set_irq(s->irqs[RTC_ISA_IRQ], level);
>           }
>       }