Re: [PATCH] irqchip/gic-v4: fix occasional VLPI drop

[Heyi Guo]

On 2019/1/24 18:33, Marc Zyngier wrote:
> On Wed, 23 Jan 2019 08:59:08 +0000,
> Heyi Guo <guoheyi@xxxxxxxxxx> wrote:
> > 1. In current implementation, every VLPI will temporarily be mapped to
> > the first CPU in system (normally CPU0) and then moved to the real
> > scheduled CPU later.
> >
> > 2. So there is a time window and a VLPI may be sent to CPU0 instead of
> > the real scheduled vCPU, in a multi-CPU virtual machine.
> >
> > 3. However, CPU0 may have not been scheduled as a virtual CPU after
> > system boots up, so the value of its GICR_VPROPBASER is unknown at
> > that moment.
> >
> > 4. If the INTID of VLPI is larger than 2^(GICR_VPROPBASER.IDbits+1),
> > while IDbits is also in unknown state, GIC will behave as if the VLPI
> > is out of range and simply drop it, which results in interrupt missing
> > in Guest.
> >
> > As no code will clear GICR_VPROPBASER at runtime, we can safely
> > initialize the IDbits field at boot time for each CPU to get rid of
> > this issue.
> >
> > We also clear Valid bit of GICR_VPENDBASER in case any ancient
> > programming gets left in and causes memory corrupting.
> >
> > Signed-off-by: Heyi Guo <guoheyi@xxxxxxxxxx>
> > Signed-off-by: Heyi Guo <heyi.guo@xxxxxxxxxx>
> > ---
> >   drivers/irqchip/irq-gic-v3-its.c | 25 +++++++++++++++++++++++++
> >   1 file changed, 25 insertions(+)
> >
> > diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> > index 3365d44..634c8a7 100644
> > --- a/drivers/irqchip/irq-gic-v3-its.c
> > +++ b/drivers/irqchip/irq-gic-v3-its.c
> > @@ -2145,6 +2145,31 @@ static void its_cpu_init_lpis(void)
> >   	val |= GICR_CTLR_ENABLE_LPIS;
> >   	writel_relaxed(val, rbase + GICR_CTLR);
> >   
> > +	if (gic_rdists->has_vlpis) {
> > +		void __iomem *vlpi_base = gic_data_rdist_vlpi_base();
> > +
> > +		/*
> > +		 * It's possible for CPU to receive VLPIs before it is
> > +		 * sheduled as a vPE, especially for the first CPU, and the
> > +		 * VLPI with INTID larger than 2^(IDbits+1) will be considered
> > +		 * as out of range and dropped by GIC.
> > +		 * So we initialize IDbits to known value to avoid VLPI drop.
> > +		 */
> > +		val = (LPI_NRBITS - 1) & GICR_VPROPBASER_IDBITS_MASK;
> > +		pr_debug("GICv4: CPU%d: Init IDbits to 0x%llx for GICR_VPROPBASER\n",
> > +			smp_processor_id(), val);
> > +		gits_write_vpropbaser(val, vlpi_base + GICR_VPROPBASER);
> > +
> > +		/*
> > +		 * Also clear Valid bit of GICR_VPENDBASER, in case some
> > +		 * ancient programming gets left in and has possibility of
> > +		 * corrupting memory.
> > +		 */
> > +		val = gits_read_vpendbaser(vlpi_base + GICR_VPENDBASER);
> > +		val &= ~GICR_VPENDBASER_Valid;
> > +		gits_write_vpendbaser(val, vlpi_base + GICR_VPENDBASER);
> I'm afraid it is not enough to just write back with the valid bit
> clear. You need to make sure Dirty has been cleared before continuing,
> which is why I was asking you to reuse some bits of its_vpe_deschedule.
>
> Something like this:
>
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index db20e992a40f..1808cb5f6a3e 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -2751,9 +2751,8 @@ static void its_vpe_schedule(struct its_vpe *vpe)
>   	gits_write_vpendbaser(val, vlpi_base + GICR_VPENDBASER);
>   }
>   
> -static void its_vpe_deschedule(struct its_vpe *vpe)
> +static u64 its_clear_vpend_valid(void __iomem *vlpi_base)
>   {
> -	void __iomem *vlpi_base = gic_data_rdist_vlpi_base();
>   	u32 count = 1000000;	/* 1s! */
>   	bool clean;
>   	u64 val;
> @@ -2773,7 +2772,17 @@ static void its_vpe_deschedule(struct its_vpe *vpe)
>   		}
>   	} while (!clean && count);
>   
> -	if (unlikely(!clean && !count)) {
> +	return val;
> +}
> +
> +static void its_vpe_deschedule(struct its_vpe *vpe)
> +{
> +	void __iomem *vlpi_base = gic_data_rdist_vlpi_base();
> +	u64 val;
> +
> +	val = its_clear_vpend_valid(vlpi_base);
> +
> +	if (unlikely(val & GICR_VPENDBASER_Dirty)) {
>   		pr_err_ratelimited("ITS virtual pending table not cleaning\n");
>   		vpe->idai = false;
>   		vpe->pending_last = true;
>
> And you can the rewrite the above GICR_VPENDBASER_Valid clearing as:
>
> 	val = its_clear_vpend_valid(vlpi_base);
> 	WARN_ON(val & GICR_VPENDBASER_Dirty);
>
> We'll at least get a warning if something goes wrong.
Got it. Will send a v2 ASAP :)

Thanks,

Heyi
> Thanks,
>
> 	M.