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Date:   Tue, 29 Jan 2019 08:12:49 +0000
Message-ID: <86bm3zvq4e.wl-marc.zyngier@arm.com>
From:   Marc Zyngier <marc.zyngier@arm.com>
To:     Heyi Guo <guoheyi@huawei.com>
Cc:     <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jason Cooper <jason@lakedaemon.net>,
        <wanghaibin.wang@huawei.com>, <yangyingliang@huawei.com>
Subject: Re: [PATCH v2] irqchip/gic-v4: fix occasional VLPI drop
In-Reply-To: <80e52297-b2b3-ef90-4626-be3819afbf92@huawei.com>
References: <1548337028-21801-1-git-send-email-guoheyi@huawei.com>
        <80e52297-b2b3-ef90-4626-be3819afbf92@huawei.com>
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On Tue, 29 Jan 2019 01:32:55 +0000,
Heyi Guo <guoheyi@huawei.com> wrote:
> 
> Hi Marc,
> 
> Any comments?

None so far, I've queued this to let it soak, and will send it as a
fix if nothing else breaks.

Thanks,

	M.

> 
> Thanks,
> 
> Heyi
> 
> 
> On 2019/1/24 21:37, Heyi Guo 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. A new function
> > its_clear_vpend_valid() is added to reuse the code in
> > its_vpe_deschedule().
> > 
> > Signed-off-by: Heyi Guo <guoheyi@huawei.com>
> > Signed-off-by: Heyi Guo <heyi.guo@linaro.org>
> > ---
> > 
> > Notes:
> >      v2:
> >      - Also wait GICR_VPENDBASER.Dirty bit to be 0 in initialization [Marc]
> >      - Add a new function to reuse the code in its_vpe_deschedule() [Marc]
> > 
> >   drivers/irqchip/irq-gic-v3-its.c | 66 +++++++++++++++++++++++++++++-----------
> >   1 file changed, 49 insertions(+), 17 deletions(-)
> > 
> > diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> > index 3365d44..531e945 100644
> > --- a/drivers/irqchip/irq-gic-v3-its.c
> > +++ b/drivers/irqchip/irq-gic-v3-its.c
> > @@ -2060,6 +2060,29 @@ static int __init allocate_lpi_tables(void)
> >   	return 0;
> >   }
> >   +static u64 its_clear_vpend_valid(void __iomem *vlpi_base)
> > +{
> > +	u32 count = 1000000;	/* 1s! */
> > +	bool clean;
> > +	u64 val;
> > +
> > +	val = gits_read_vpendbaser(vlpi_base + GICR_VPENDBASER);
> > +	val &= ~GICR_VPENDBASER_Valid;
> > +	gits_write_vpendbaser(val, vlpi_base + GICR_VPENDBASER);
> > +
> > +	do {
> > +		val = gits_read_vpendbaser(vlpi_base + GICR_VPENDBASER);
> > +		clean = !(val & GICR_VPENDBASER_Dirty);
> > +		if (!clean) {
> > +			count--;
> > +			cpu_relax();
> > +			udelay(1);
> > +		}
> > +	} while (!clean && count);
> > +
> > +	return val;
> > +}
> > +
> >   static void its_cpu_init_lpis(void)
> >   {
> >   	void __iomem *rbase = gic_data_rdist_rd_base();
> > @@ -2145,6 +2168,30 @@ 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 = its_clear_vpend_valid(vlpi_base);
> > +		WARN_ON(val & GICR_VPENDBASER_Dirty);
> > +	}
> > +
> >   	/* Make sure the GIC has seen the above */
> >   	dsb(sy);
> >   out:
> > @@ -2757,26 +2804,11 @@ static void its_vpe_schedule(struct its_vpe *vpe)
> >   static void its_vpe_deschedule(struct its_vpe *vpe)
> >   {
> >   	void __iomem *vlpi_base = gic_data_rdist_vlpi_base();
> > -	u32 count = 1000000;	/* 1s! */
> > -	bool clean;
> >   	u64 val;
> >   -	/* We're being scheduled out */
> > -	val = gits_read_vpendbaser(vlpi_base + GICR_VPENDBASER);
> > -	val &= ~GICR_VPENDBASER_Valid;
> > -	gits_write_vpendbaser(val, vlpi_base + GICR_VPENDBASER);
> > -
> > -	do {
> > -		val = gits_read_vpendbaser(vlpi_base + GICR_VPENDBASER);
> > -		clean = !(val & GICR_VPENDBASER_Dirty);
> > -		if (!clean) {
> > -			count--;
> > -			cpu_relax();
> > -			udelay(1);
> > -		}
> > -	} while (!clean && count);
> > +	val = its_clear_vpend_valid(vlpi_base);
> >   -	if (unlikely(!clean && !count)) {
> > +	if (unlikely(val & GICR_VPENDBASER_Dirty)) {
> >   		pr_err_ratelimited("ITS virtual pending table not cleaning\n");
> >   		vpe->idai = false;
> >   		vpe->pending_last = true;
> 
> 

-- 
Jazz is not dead, it just smell funny.