linux-kernel - Re: [PATCH v2 3/7] s390/pci: Use dma-iommu layer

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Message-ID: <bc1e4fd5-bf96-f579-8190-fda9b41d1547@arm.com>
Date:   Mon, 28 Nov 2022 18:03:51 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Gerd Bayer <gbayer@...ux.ibm.com>, iommu@...ts.linux.dev,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Wenjia Zhang <wenjia@...ux.ibm.com>
Cc:     Pierre Morel <pmorel@...ux.ibm.com>, linux-s390@...r.kernel.org,
        borntraeger@...ux.ibm.com, hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        svens@...ux.ibm.com, linux-kernel@...r.kernel.org,
        Julian Ruess <julianr@...ux.ibm.com>
Subject: Re: [PATCH v2 3/7] s390/pci: Use dma-iommu layer

On 2022-11-16 17:16, Niklas Schnelle wrote:
[...]
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index dc5f7a156ff5..804fb8f42d61 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -93,7 +93,7 @@ config IOMMU_DEBUGFS
>   choice
>   	prompt "IOMMU default domain type"
>   	depends on IOMMU_API
> -	default IOMMU_DEFAULT_DMA_LAZY if X86 || IA64
> +	default IOMMU_DEFAULT_DMA_LAZY if X86 || IA64 || S390
>   	default IOMMU_DEFAULT_DMA_STRICT
>   	help
>   	  Choose the type of IOMMU domain used to manage DMA API usage by
> @@ -412,6 +412,7 @@ config ARM_SMMU_V3_SVA
>   config S390_IOMMU
>   	def_bool y if S390 && PCI
>   	depends on S390 && PCI
> +	select IOMMU_DMA

Please add S390 to the condition under config IOMMU_DMA instead.

>   	select IOMMU_API
>   	help
>   	  Support for the IOMMU API for s390 PCI devices.
[...]
> @@ -45,9 +329,14 @@ static struct iommu_domain *s390_domain_alloc(unsigned domain_type)
>   {
>   	struct s390_domain *s390_domain;
>   
> -	if (domain_type != IOMMU_DOMAIN_UNMANAGED)
> +	switch (domain_type) {
> +	case IOMMU_DOMAIN_DMA:
> +	case IOMMU_DOMAIN_DMA_FQ:

I was about to question adding this without any visible treatment of 
iommu_iotlb_gather_queued() or domain->type == IOMMU_DOMAIN_DMA_FQ as a 
whole, but I guess if you never actually free any pagetables it does 
work out OK. Bit of a timebomb if there's a chance of that ever changing 
in future, though.

> +	case IOMMU_DOMAIN_UNMANAGED:
> +		break;
> +	default:
>   		return NULL;
> -
> +	}
>   	s390_domain = kzalloc(sizeof(*s390_domain), GFP_KERNEL);
>   	if (!s390_domain)
>   		return NULL;
[...]
> @@ -397,12 +678,29 @@ static size_t s390_iommu_unmap_pages(struct iommu_domain *domain,
>   		return 0;
>   
>   	iommu_iotlb_gather_add_range(gather, iova, size);
> +	atomic64_add(pgcount, &s390_domain->ctrs.unmapped_pages);
>   
>   	return size;
>   }
>   
> +static void s390_iommu_probe_finalize(struct device *dev)
> +{
> +	struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
> +
> +	iommu_dma_forcedac = true;
> +	iommu_setup_dma_ops(dev, domain->geometry.aperture_start, domain->geometry.aperture_end);

For consistency with all but one other caller now, just pass 0 and 
U64_MAX for base and size to make it clear that they're meaningless 
(they will eventually go away as part of a bigger refactoring).

Thanks,
Robin.