Re: [PATCH v2 1/2] LoongArch: Fix AP booting issue in VM mode

[maobibo <maobibo@xxxxxxxxxxx>]

ping.


On 2024/8/15 下午3:15, Bibo Mao wrote:
> Native IPI is used for AP booting, it is booting interface between
> OS and BIOS firmware. The paravirt ipi is only used inside OS, native
> IPI is necessary to boot AP.
>
> When booting AP, BP writes kernel entry address in the HW mailbox of
> AP and send IPI interrupt to AP. AP executes idle instruction and
> waits for interrupt or SW events, and clears IPI interrupt and jumps
> to kernel entry from HW mailbox.
>
> Between BP writes HW mailbox and is ready to send IPI to AP, AP is woken
> up by SW events and jumps to kernel entry, so ACTION_BOOT_CPU IPI
> interrupt will keep pending during AP booting. And native IPI interrupt
> handler needs be registered so that it can clear pending native IPI, else
> there will be endless IRQ handling during AP booting stage.
>
> Here native ipi interrupt is initialized even if paravirt IPI is used.
>
> Fixes: 74c16b2e2b0c ("LoongArch: KVM: Add PV IPI support on guest side")
>
> Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx>
> ---
>   arch/loongarch/kernel/paravirt.c | 19 +++++++++++++++++++
>   1 file changed, 19 insertions(+)
>
> diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
> index 9c9b75b76f62..348920b25460 100644
> --- a/arch/loongarch/kernel/paravirt.c
> +++ b/arch/loongarch/kernel/paravirt.c
> @@ -13,6 +13,9 @@ static int has_steal_clock;
>   struct static_key paravirt_steal_enabled;
>   struct static_key paravirt_steal_rq_enabled;
>   static DEFINE_PER_CPU(struct kvm_steal_time, steal_time) __aligned(64);
> +#ifdef CONFIG_SMP
> +static struct smp_ops old_ops;
> +#endif
>   
>   static u64 native_steal_clock(int cpu)
>   {
> @@ -55,6 +58,11 @@ static void pv_send_ipi_single(int cpu, unsigned int action)
>   	int min, old;
>   	irq_cpustat_t *info = &per_cpu(irq_stat, cpu);
>   
> +	if (unlikely(action == ACTION_BOOT_CPU)) {
> +		old_ops.send_ipi_single(cpu, action);
> +		return;
> +	}
> +
>   	old = atomic_fetch_or(BIT(action), &info->message);
>   	if (old)
>   		return;
> @@ -71,6 +79,12 @@ static void pv_send_ipi_mask(const struct cpumask *mask, unsigned int action)
>   	__uint128_t bitmap = 0;
>   	irq_cpustat_t *info;
>   
> +	if (unlikely(action == ACTION_BOOT_CPU)) {
> +		/* Use native IPI to boot AP */
> +		old_ops.send_ipi_mask(mask, action);
> +		return;
> +	}
> +
>   	if (cpumask_empty(mask))
>   		return;
>   
> @@ -141,6 +155,8 @@ static void pv_init_ipi(void)
>   {
>   	int r, swi;
>   
> +	/* Init native ipi irq since AP booting uses it */
> +	old_ops.init_ipi();
>   	swi = get_percpu_irq(INT_SWI0);
>   	if (swi < 0)
>   		panic("SWI0 IRQ mapping failed\n");
> @@ -179,6 +195,9 @@ int __init pv_ipi_init(void)
>   		return 0;
>   
>   #ifdef CONFIG_SMP
> +	old_ops.init_ipi	= mp_ops.init_ipi;
> +	old_ops.send_ipi_single = mp_ops.send_ipi_single;
> +	old_ops.send_ipi_mask	= mp_ops.send_ipi_mask;
>   	mp_ops.init_ipi		= pv_init_ipi;
>   	mp_ops.send_ipi_single	= pv_send_ipi_single;
>   	mp_ops.send_ipi_mask	= pv_send_ipi_mask;