Re: [PATCH v2 03/10] irqchip/gic-v5: Serialise IRS synchronisation requests

[Lorenzo Pieralisi <lpieralisi@kernel.org>]

[Remove stable from the CC email recipient list, leave it only in the log]

On Wed, Nov 04, 2026 at 05:47:57PM +0000, Sascha Bischoff wrote:
> IRS_SYNCR writes are ignored while IRS_SYNC_STATUSR.IDLE is clear.
> Calls to gicv5_irs_syncr() for different IRQs can overlap, allowing

Nit: gicv5_irs_syncr() has no notion of specific IRQs, this is
misleading.

> the second request to be dropped. Its caller can then observe the
> first request completing and assume that its own events have been
> processed.
> 
> With GICv5 ITS KVM support, gicv5_irs_syncr() is also called while
> restoring the host ITTE in gicv5_its_set_vcpu_affinity(). The callback
> runs under the IRQ descriptor lock via irq_set_vcpu_affinity(), so it
> cannot sleep.

Technically we are talking about a use case that does not exist yet.

I understand it is churn to fix it first and change it again later,
I would just say that gicv5_irs_syncr() might need to be called in atomic
context.

> Serialise the request and completion poll with a raw spinlock, and use
> atomic polling because the synchronisation runs while holding the IRQ
> descriptor lock.
> 
> Fixes: 57d72196dfc8 ("irqchip/gic-v5: Add GICv5 ITS support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sascha Bischoff <sascha.bischoff@arm.com>
> ---
>  drivers/irqchip/irq-gic-v5-irs.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v5-irs.c b/drivers/irqchip/irq-gic-v5-irs.c
> index 4edf787f3f97f..ead76560ea08f 100644
> --- a/drivers/irqchip/irq-gic-v5-irs.c
> +++ b/drivers/irqchip/irq-gic-v5-irs.c
> @@ -10,6 +10,7 @@
>  #include <linux/log2.h>
>  #include <linux/of.h>
>  #include <linux/of_address.h>
> +#include <linux/spinlock.h>
>  
>  #include <linux/irqchip.h>
>  #include <linux/irqchip/arm-gic-v5.h>
> @@ -22,6 +23,8 @@
>  #define LPI_ID_BITS_LINEAR		12
>  
>  static DEFINE_PER_CPU_READ_MOSTLY(struct gicv5_irs_chip_data *, per_cpu_irs_data);
> +/* Synchronization requests must not overlap in an IRS Domain. */
> +static DEFINE_RAW_SPINLOCK(irs_sync_lock);
>  static LIST_HEAD(irs_nodes);
>  
>  static u32 irs_readl_relaxed(struct gicv5_irs_chip_data *irs_data,
> @@ -507,10 +510,11 @@ void gicv5_irs_syncr(void)
>  		return;
>  
>  	syncr = FIELD_PREP(GICV5_IRS_SYNCR_SYNC, 1);
> +	guard(raw_spinlock_irqsave)(&irs_sync_lock);
>  	irs_writel_relaxed(irs_data, syncr, GICV5_IRS_SYNCR);
>  
> -	gicv5_wait_for_op(irs_data->irs_base, GICV5_IRS_SYNC_STATUSR,
> -			  GICV5_IRS_SYNC_STATUSR_IDLE);
> +	gicv5_wait_for_op_atomic(irs_data->irs_base, GICV5_IRS_SYNC_STATUSR,
> +				 GICV5_IRS_SYNC_STATUSR_IDLE, NULL);
>  }

Acked-by: Lorenzo Pieralisi <lpieralisi@kernel.org>

>  
>  int gicv5_irs_register_cpu(int cpuid)
> 
> -- 
> 2.34.1
>