linux-kernel - Re: [PATCH v2] irqchip/gic-v4: fix occasional VLPI drop

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Date:   Tue, 29 Jan 2019 09:32:55 +0800
From:   Heyi Guo <guoheyi@...wei.com>
To:     Marc Zyngier <marc.zyngier@....com>
CC:     <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        <wanghaibin.wang@...wei.com>, <yangyingliang@...wei.com>
Subject: Re: [PATCH v2] irqchip/gic-v4: fix occasional VLPI drop

Hi Marc,

Any comments?

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@...wei.com>
> Signed-off-by: Heyi Guo <heyi.guo@...aro.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;