Peter Maydell <[email protected]> writes:
> On Fri, 29 May 2026 at 09:29, Alex Bennée <[email protected]> wrote:
>>
>> This series fully models the behaviour of WFxT instructions. We
>> already had support for WFE for M-profile but we left off A-profile as
>> it has more potential sources of wake-ups. The main one is the event
>> stream which includes events from significant bits of the timer
>> ticking over.
>>
>> The refactoring from the previous iterations of the patch have now
>> been merged.
>>
>> I've dropped trying to fully model the global monitor in favour of
>> taking advantage of the architectural flexibility to have an IMPDEF
>> event wake up for any reason. We treat the setting of exclusive_addr
>> as such a reason because it indicates the current vCPU is in a ldstx
>> exclusive region and we don't want the guest to deadlock. This does mean
>> the system won't sleep on WFE enabled locks but people shouldn't be
>> relying on QEMU to model real world sleep patterns anyway given the
>> efficiency of emulation compared to real HW.
>>
>> I've written a test case using kvm-unit-tests:
>>
>> Message-ID: <[email protected]>
>> Date: Wed, 27 May 2026 12:18:21 +0100
>> Subject: [kvm-unit-tests PATCH v2] arm: add wfx test case
>> From: =?UTF-8?q?Alex=20Benn=C3=A9e?= <[email protected]>
>>
>> All patches are now reviewed.
>
>
>
> Applied to target-arm.next, thanks.
Is it too late to drop them? I've a fix for 2/8:
--8<---------------cut here---------------start------------->8---
modified include/hw/core/sysemu-cpu-ops.h
@@ -18,6 +18,9 @@
typedef struct SysemuCPUOps {
/**
* @has_work: Callback for checking if there is work to do.
+ *
+ * This function should be idempotent (i.e. not change state) as
+ * it will likely be queried multiple times before a CPU resumes.
*/
bool (*has_work)(CPUState *cpu); /* MANDATORY NON-NULL */
/**
modified target/arm/cpu.c
@@ -158,7 +158,6 @@ static bool arm_cpu_has_work(CPUState *cs)
* A wake-up event should only wake us if we are halted on a WFE
*/
if (cpu->env.halt_reason == HALT_WFE && cpu->env.event_register) {
- cpu->env.halt_reason = NOT_HALTED;
return true;
}
@@ -170,7 +169,6 @@ static bool arm_cpu_has_work(CPUState *cs)
| CPU_INTERRUPT_NMI | CPU_INTERRUPT_VINMI |
CPU_INTERRUPT_VFNMI
| CPU_INTERRUPT_VFIQ | CPU_INTERRUPT_VIRQ |
CPU_INTERRUPT_VSERR
| CPU_INTERRUPT_EXITTB)) {
- cpu->env.halt_reason = NOT_HALTED;
return true;
}
@@ -874,6 +872,8 @@ bool arm_cpu_exec_halt(CPUState *cs)
if (cpu->wfxt_timer) {
timer_del(cpu->wfxt_timer);
}
+ /* clear the halt reason */
+ cpu->env.halt_reason = NOT_HALTED;
}
return leave_halt;
}
--8<---------------cut here---------------end--------------->8---
>
> -- PMM
--
Alex Bennée
Virtualisation Tech Lead @ Linaro
