Re: [PATCH v12 1/7] irqchip/gic-v3: Enable support for SGIs to act as NMIs

[Mark Rutland]

On Wed, Aug 30, 2023 at 12:11:22PM -0700, Douglas Anderson wrote:
> As of commit 6abbd6988971 ("irqchip/gic, gic-v3: Make SGIs use
> handle_percpu_devid_irq()") SGIs are treated the same as PPIs/EPPIs
> and use handle_percpu_devid_irq() by default. Unfortunately,
> handle_percpu_devid_irq() isn't NMI safe, and so to run in an NMI
> context those should use handle_percpu_devid_fasteoi_nmi().
> 
> In order to accomplish this, we just have to make room for SGIs in the
> array of refcounts that keeps track of which interrupts are set as
> NMI. We also rename the array and create a new indexing scheme that
> accounts for SGIs.
> 
> Also, enable NMI support prior to gic_smp_init() as allocation of SGIs
> as IRQs/NMIs happen as part of this routine.
> 
> Co-developed-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
> Signed-off-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
> ---
> I'll note that this change is a little more black magic to me than
> others in this series. I don't have a massive amounts of familiarity
> with all the moving parts of gic-v3, so I mostly just followed Mark
> Rutland's advice [1]. Please pay extra attention to make sure I didn't
> do anything too terrible.
> 
> Mark's advice wasn't a full patch and I ended up doing a bit of work
> to translate it to reality, so I did not add him as "Co-developed-by"
> here. Mark: if you would like this tag then please provide it and your
> Signed-off-by. I certainly won't object.

That's all reasonable, and I'm perfectly happy without a tag.

I have one trivial nit below, but with or without that fixed up:

Acked-by: Mark Rutland <mark.rutland@xxxxxxx>

> 
> [1] https://lore.kernel.org/r/ZNC-YRQopO0PaIIo@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> 
> Changes in v12:
> - Added a comment about why we account for 16 SGIs when Linux uses 8.
> 
> Changes in v10:
> - Rewrite as needed for 5.11+ as per Mark Rutland and Sumit.
> 
>  drivers/irqchip/irq-gic-v3.c | 59 +++++++++++++++++++++++++-----------
>  1 file changed, 41 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index eedfa8e9f077..8d20122ba0a8 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -78,6 +78,13 @@ static DEFINE_STATIC_KEY_TRUE(supports_deactivate_key);
>  #define GIC_LINE_NR	min(GICD_TYPER_SPIS(gic_data.rdists.gicd_typer), 1020U)
>  #define GIC_ESPI_NR	GICD_TYPER_ESPIS(gic_data.rdists.gicd_typer)
>  
> +/*
> + * There are 16 SGIs, though we only actually use 8 in Linux. The other 8 SGIs
> + * are potentially stolen by the secure side. Some code, especially code dealing
> + * with hwirq IDs, is simplified by accounting for all 16.
> + */
> +#define SGI_NR		16
> +
>  /*
>   * The behaviours of RPR and PMR registers differ depending on the value of
>   * SCR_EL3.FIQ, and the behaviour of non-secure priority registers of the
> @@ -125,8 +132,8 @@ EXPORT_SYMBOL(gic_nonsecure_priorities);
>  		__priority;						\
>  	})
>  
> -/* ppi_nmi_refs[n] == number of cpus having ppi[n + 16] set as NMI */
> -static refcount_t *ppi_nmi_refs;
> +/* rdist_nmi_refs[n] == number of cpus having the rdist interrupt n set as NMI */
> +static refcount_t *rdist_nmi_refs;
>  
>  static struct gic_kvm_info gic_v3_kvm_info __initdata;
>  static DEFINE_PER_CPU(bool, has_rss);
> @@ -519,9 +526,22 @@ static u32 __gic_get_ppi_index(irq_hw_number_t hwirq)
>  	}
>  }
>  
> -static u32 gic_get_ppi_index(struct irq_data *d)
> +static u32 __gic_get_rdist_idx(irq_hw_number_t hwirq)
> +{
> +	switch (__get_intid_range(hwirq)) {
> +	case SGI_RANGE:
> +	case PPI_RANGE:
> +		return hwirq;
> +	case EPPI_RANGE:
> +		return hwirq - EPPI_BASE_INTID + 32;
> +	default:
> +		unreachable();
> +	}
> +}
> +
> +static u32 gic_get_rdist_idx(struct irq_data *d)
>  {
> -	return __gic_get_ppi_index(d->hwirq);
> +	return __gic_get_rdist_idx(d->hwirq);
>  }

Nit: It would be nicer to call this gic_get_rdist_index() to match
gic_get_ppi_index(); likewise with __gic_get_rdist_index().

That's my fault given I suggested the gic_get_rdist_idx() name in:

  https://lore.kernel.org/linux-arm-kernel/ZNC-YRQopO0PaIIo@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/

... so sorry about that!

Mark.

>  
>  static int gic_irq_nmi_setup(struct irq_data *d)
> @@ -545,11 +565,14 @@ static int gic_irq_nmi_setup(struct irq_data *d)
>  
>  	/* desc lock should already be held */
>  	if (gic_irq_in_rdist(d)) {
> -		u32 idx = gic_get_ppi_index(d);
> +		u32 idx = gic_get_rdist_idx(d);
>  
> -		/* Setting up PPI as NMI, only switch handler for first NMI */
> -		if (!refcount_inc_not_zero(&ppi_nmi_refs[idx])) {
> -			refcount_set(&ppi_nmi_refs[idx], 1);
> +		/*
> +		 * Setting up a percpu interrupt as NMI, only switch handler
> +		 * for first NMI
> +		 */
> +		if (!refcount_inc_not_zero(&rdist_nmi_refs[idx])) {
> +			refcount_set(&rdist_nmi_refs[idx], 1);
>  			desc->handle_irq = handle_percpu_devid_fasteoi_nmi;
>  		}
>  	} else {
> @@ -582,10 +605,10 @@ static void gic_irq_nmi_teardown(struct irq_data *d)
>  
>  	/* desc lock should already be held */
>  	if (gic_irq_in_rdist(d)) {
> -		u32 idx = gic_get_ppi_index(d);
> +		u32 idx = gic_get_rdist_idx(d);
>  
>  		/* Tearing down NMI, only switch handler for last NMI */
> -		if (refcount_dec_and_test(&ppi_nmi_refs[idx]))
> +		if (refcount_dec_and_test(&rdist_nmi_refs[idx]))
>  			desc->handle_irq = handle_percpu_devid_irq;
>  	} else {
>  		desc->handle_irq = handle_fasteoi_irq;
> @@ -1279,10 +1302,10 @@ static void gic_cpu_init(void)
>  	rbase = gic_data_rdist_sgi_base();
>  
>  	/* Configure SGIs/PPIs as non-secure Group-1 */
> -	for (i = 0; i < gic_data.ppi_nr + 16; i += 32)
> +	for (i = 0; i < gic_data.ppi_nr + SGI_NR; i += 32)
>  		writel_relaxed(~0, rbase + GICR_IGROUPR0 + i / 8);
>  
> -	gic_cpu_config(rbase, gic_data.ppi_nr + 16, gic_redist_wait_for_rwp);
> +	gic_cpu_config(rbase, gic_data.ppi_nr + SGI_NR, gic_redist_wait_for_rwp);
>  
>  	/* initialise system registers */
>  	gic_cpu_sys_reg_init();
> @@ -1939,12 +1962,13 @@ static void gic_enable_nmi_support(void)
>  		return;
>  	}
>  
> -	ppi_nmi_refs = kcalloc(gic_data.ppi_nr, sizeof(*ppi_nmi_refs), GFP_KERNEL);
> -	if (!ppi_nmi_refs)
> +	rdist_nmi_refs = kcalloc(gic_data.ppi_nr + SGI_NR,
> +				 sizeof(*rdist_nmi_refs), GFP_KERNEL);
> +	if (!rdist_nmi_refs)
>  		return;
>  
> -	for (i = 0; i < gic_data.ppi_nr; i++)
> -		refcount_set(&ppi_nmi_refs[i], 0);
> +	for (i = 0; i < gic_data.ppi_nr + SGI_NR; i++)
> +		refcount_set(&rdist_nmi_refs[i], 0);
>  
>  	pr_info("Pseudo-NMIs enabled using %s ICC_PMR_EL1 synchronisation\n",
>  		gic_has_relaxed_pmr_sync() ? "relaxed" : "forced");
> @@ -2061,6 +2085,7 @@ static int __init gic_init_bases(phys_addr_t dist_phys_base,
>  
>  	gic_dist_init();
>  	gic_cpu_init();
> +	gic_enable_nmi_support();
>  	gic_smp_init();
>  	gic_cpu_pm_init();
>  
> @@ -2073,8 +2098,6 @@ static int __init gic_init_bases(phys_addr_t dist_phys_base,
>  			gicv2m_init(handle, gic_data.domain);
>  	}
>  
> -	gic_enable_nmi_support();
> -
>  	return 0;
>  
>  out_free:
> -- 
> 2.42.0.283.g2d96d420d3-goog
>