> On 27. Apr 2026, at 21:55, Scott J. Goldman <[email protected]> wrote:
>
> Commit b5f8f77271 ("accel/hvf: Implement WFI without using pselect()")
> changed hvf_wfi() from blocking the vCPU thread with pselect() to
> returning EXCP_HLT, intending QEMU's main event loop to handle the
> idle wait. However, cpu->halted was never set, so cpu_thread_is_idle()
> always returns false and the vCPU thread spins at 100% CPU per core
> while the guest is idle.
>
> Fix this by:
>
> 1. Setting cpu->halted = 1 in hvf_wfi() so the vCPU thread sleeps on
> halt_cond in qemu_process_cpu_events().
>
> 2. Arming a per-vCPU QEMU_CLOCK_VIRTUAL timer to fire when the guest's
> virtual timer (CNTV_CVAL_EL0) would expire. This is necessary
> because HVF only delivers HV_EXIT_REASON_VTIMER_ACTIVATED during
> hv_vcpu_run(), which is not called while the CPU is halted. The
> timer callback mirrors the VTIMER_ACTIVATED handler: it raises the
> vtimer IRQ through the GIC and marks vtimer_masked, causing the
> interrupt delivery chain to wake the vCPU via qemu_cpu_kick().
>
> 3. Clearing cpu->halted in hvf_arch_vcpu_exec() when cpu_has_work()
> indicates a pending interrupt, and cancelling the WFI timer.
>
> 4. Re-arming the WFI timer from hvf_vm_state_change() on the resume
> transition for any halted vCPU, since the QEMUTimer is per-instance
> state and is not migrated. After cpu_synchronize_all_states() the
> migrated vtimer state is mirrored in env, so we can read CNTV_CTL
> and CNTV_CVAL from there. If the vtimer has already expired by the
> time the destination resumes, hvf_wfi_timer_cb() is invoked
> directly so the halted vCPU is woken up.
>
> Fixes: b5f8f77271 ("accel/hvf: Implement WFI without using pselect()")
> Signed-off-by: Scott J. Goldman <[email protected]>
Hi,
A bit of a side note for reproducing this:
To reproduce this on current master, as far as I can tell you need either
-M kernel-irqchip=off or -M virt-11.0 or earlier. -M virt(-11.1) on master uses
the HVF vGIC path.
