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Subject: Re: [PATCH v5 01/23] irqchip/gic-v3: Use SGIs without active state if
 offered
To:     Marc Zyngier <maz@kernel.org>,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Jason Cooper <jason@lakedaemon.net>,
        Robert Richter <rrichter@marvell.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Zenghui Yu <yuzenghui@huawei.com>,
        James Morse <james.morse@arm.com>,
        Julien Thierry <julien.thierry.kdev@gmail.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>
References: <20200304203330.4967-1-maz@kernel.org>
 <20200304203330.4967-2-maz@kernel.org>
From:   Auger Eric <eric.auger@redhat.com>
Message-ID: <1fa8ab2f-6766-9dc1-53a6-9cead19a5a7b@redhat.com>
Date:   Thu, 12 Mar 2020 18:16:45 +0100
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Hi Marc,

On 3/4/20 9:33 PM, Marc Zyngier wrote:
> To allow the direct injection of SGIs into a guest, the GICv4.1
> architecture has to sacrifice the Active state so that SGIs look
> a lot like LPIs (they are injected by the same mechanism).
> 
> In order not to break existing software, the architecture gives
> offers guests OSs the choice: SGIs with or without an active
nit gives offers
> state. It is the hypervisors duty to honor the guest's choice.
> 
> For this, the architecture offers a discovery bit indicating whether
> the GIC supports GICv4.1 SGIs (GICD_TYPER2.nASSGIcap), and another
> bit indicating whether the guest wants Active-less SGIs or not
> (controlled by GICD_CTLR.nASSGIreq).
> 
> A hypervisor not supporting GICv4.1 SGIs would leave nASSGIcap
> clear, and a guest not knowing about GICv4.1 SGIs (or definitely
> wanting an Active state) would leave nASSGIreq clear (both being
> thankfully backward compatible with older revisions of the GIC).
> 
> Since Linux is perfectly happy without an active state on SGIs,
> inform the hypervisor that we'll use that if offered.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Reviewed-by: Zenghui Yu <yuzenghui@huawei.com>
> ---
>  drivers/irqchip/irq-gic-v3.c       | 10 ++++++++--
>  include/linux/irqchip/arm-gic-v3.h |  2 ++
>  2 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index cd76435c4a31..73e87e176d76 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -724,6 +724,7 @@ static void __init gic_dist_init(void)
>  	unsigned int i;
>  	u64 affinity;
>  	void __iomem *base = gic_data.dist_base;
> +	u32 val;
>  
>  	/* Disable the distributor */
>  	writel_relaxed(0, base + GICD_CTLR);
> @@ -756,9 +757,14 @@ static void __init gic_dist_init(void)
>  	/* Now do the common stuff, and wait for the distributor to drain */
>  	gic_dist_config(base, GIC_LINE_NR, gic_dist_wait_for_rwp);
>  
> +	val = GICD_CTLR_ARE_NS | GICD_CTLR_ENABLE_G1A | GICD_CTLR_ENABLE_G1;
> +	if (gic_data.rdists.gicd_typer2 & GICD_TYPER2_nASSGIcap) {
> +		pr_info("Enabling SGIs without active state\n");
> +		val |= GICD_CTLR_nASSGIreq;
> +	}
> +
>  	/* Enable distributor with ARE, Group1 */
> -	writel_relaxed(GICD_CTLR_ARE_NS | GICD_CTLR_ENABLE_G1A | GICD_CTLR_ENABLE_G1,
> -		       base + GICD_CTLR);
> +	writel_relaxed(val, base + GICD_CTLR);
>  
>  	/*
>  	 * Set all global interrupts to the boot CPU only. ARE must be
> diff --git a/include/linux/irqchip/arm-gic-v3.h b/include/linux/irqchip/arm-gic-v3.h
> index 83439bfb6c5b..c29a02678a6f 100644
> --- a/include/linux/irqchip/arm-gic-v3.h
> +++ b/include/linux/irqchip/arm-gic-v3.h
> @@ -57,6 +57,7 @@
>  #define GICD_SPENDSGIR			0x0F20
>  
>  #define GICD_CTLR_RWP			(1U << 31)
> +#define GICD_CTLR_nASSGIreq		(1U << 8)
I am not able to find this bit in Arm IHI 0069F (ID022020)
same for the bit in GICD_TYPER. Do we still miss part of the spec?

Thanks

Eric
>  #define GICD_CTLR_DS			(1U << 6)
>  #define GICD_CTLR_ARE_NS		(1U << 4)
>  #define GICD_CTLR_ENABLE_G1A		(1U << 1)
> @@ -90,6 +91,7 @@
>  #define GICD_TYPER_ESPIS(typer)						\
>  	(((typer) & GICD_TYPER_ESPI) ? GICD_TYPER_SPIS((typer) >> 27) : 0)
>  
> +#define GICD_TYPER2_nASSGIcap		(1U << 8)
>  #define GICD_TYPER2_VIL			(1U << 7)
>  #define GICD_TYPER2_VID			GENMASK(4, 0)
>  
>