Re: [PATCH for-4.21?] AMD/IOMMU: unshare IRQ .ack and .disable handlers

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Oct 20, 2025 at 04:16:13PM +0200, Jan Beulich wrote:
> A .disable handler can't typically be re-used for .ack: The latter needs
> to deal with IRQ migration, while the former shouldn't. Furthermore
> invoking just irq_complete_move() isn't enough; one of
> move_{native,masked}_irq() also need invoking.
> 
> Fixes: 487a1cffd71a ("x86: Implement per-cpu vector for xen hypervisor")
> Fixes: f821102450a1 ("x86: IRQ Migration logic enhancement")
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> --- a/xen/drivers/passthrough/amd/iommu_init.c
> +++ b/xen/drivers/passthrough/amd/iommu_init.c
> @@ -428,8 +428,6 @@ static void cf_check iommu_msi_mask(stru
>      unsigned long flags;
>      struct amd_iommu *iommu = desc->action->dev_id;
>  
> -    irq_complete_move(desc);
> -
>      spin_lock_irqsave(&iommu->lock, flags);
>      amd_iommu_msi_enable(iommu, IOMMU_CONTROL_DISABLED);
>      spin_unlock_irqrestore(&iommu->lock, flags);
> @@ -442,6 +440,13 @@ static unsigned int cf_check iommu_msi_s
>      return 0;
>  }
>  
> +static void cf_check iommu_msi_ack(struct irq_desc *desc)
> +{
> +    irq_complete_move(desc);
> +    iommu_msi_mask(desc);
> +    move_masked_irq(desc);

Not sure it matters much, as I don't expect IOMMU interrupts to move
around frequently, but do we really need to mask the source?  The
update of the interrupt would be done atomically, as we know IOMMU is
available.  Anyway this can be done later, so:

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Thanks, Roger.