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.
All wfi_timer handling (allocation, arming, deletion, and the resume
re-arm) is gated on !hvf_irqchip_in_kernel(): with the Apple in-kernel
vGIC, HVF owns the vtimer and delivers wake-ups itself.
Note for stable backports: this commit won't apply to 11.0 as
it has changes to handle the hvf in-kernel irqchip support that
landed after the 11.0 release. The v3 version of this commit:
https://patchew.org/QEMU/20260427195516.46256-1-scottjgo@gmail.com/
should be suitable for 11.0 backporting (it is essentially
identical except that it doesn't make the changes conditional
on !hvf_irqchip_in_kernel()).
Cc: qemu-stable@nongnu.org
Fixes: b5f8f77271 ("accel/hvf: Implement WFI without using pselect()")
Signed-off-by: Scott J. Goldman <scottjgo@gmail.com>
Reviewed-by: Mohamed Mediouni <mohamed@unpredictable.fr>
[PMM: added note about stable backports to commit message]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
a86024eb2d