linux-kernel - Re: [PATCH v4 6/7] iommu/dma: Centralise iommu_setup_dma

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Date: Tue, 30 Apr 2024 16:39:32 +0200
From: Niklas Schnelle <schnelle@...ux.ibm.com>
To: Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig
	 <hch@....de>
Cc: Vineet Gupta <vgupta@...nel.org>, Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Walmsley
 <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou
 <aou@...s.berkeley.edu>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Hanjun
 Guo <guohanjun@...wei.com>,
        Sudeep Holla <sudeep.holla@....com>,
        "K. Y.
 Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        Suravee
 Suthikulpanit <suravee.suthikulpanit@....com>,
        David Woodhouse
 <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Matthew Rosato
 <mjrosato@...ux.ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Rob Herring
 <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Marek
 Szyprowski <m.szyprowski@...sung.com>,
        Jason Gunthorpe <jgg@...pe.ca>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
        iommu@...ts.linux.dev, devicetree@...r.kernel.org,
        Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH v4 6/7] iommu/dma: Centralise iommu_setup_dma_ops()

On Fri, 2024-04-19 at 17:54 +0100, Robin Murphy wrote:
> It's somewhat hard to see, but arm64's arch_setup_dma_ops() should only
> ever call iommu_setup_dma_ops() after a successful iommu_probe_device(),
> which means there should be no harm in achieving the same order of
> operations by running it off the back of iommu_probe_device() itself.
> This then puts it in line with the x86 and s390 .probe_finalize bodges,
> letting us pull it all into the main flow properly. As a bonus this lets
> us fold in and de-scope the PCI workaround setup as well.
> 
> At this point we can also then pull the call up inside the group mutex,
> and avoid having to think about whether iommu_group_store_type() could
> theoretically race and free the domain if iommu_setup_dma_ops() ran just
> *before* iommu_device_use_default_domain() claims it... Furthermore we
> replace one .probe_finalize call completely, since the only remaining
> implementations are now one which only needs to run once for the initial
> boot-time probe, and two which themselves render that path unreachable.
> 
> This leaves us a big step closer to realistically being able to unpick
> the variety of different things that iommu_setup_dma_ops() has been
> muddling together, and further streamline iommu-dma into core API flows
> in future.
> 
> Reviewed-by: Lu Baolu <baolu.lu@...ux.intel.com> # For Intel IOMMU
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> Tested-by: Hanjun Guo <guohanjun@...wei.com>
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
---8<---
> diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c
> index 9a5196f523de..d8eaa7ea380b 100644
> --- a/drivers/iommu/s390-iommu.c
> +++ b/drivers/iommu/s390-iommu.c
> @@ -695,11 +695,6 @@ static size_t s390_iommu_unmap_pages(struct iommu_domain *domain,
>  	return size;
>  }
>  
> -static void s390_iommu_probe_finalize(struct device *dev)
> -{
> -	iommu_setup_dma_ops(dev, 0, U64_MAX);
> -}
> -
>  struct zpci_iommu_ctrs *zpci_get_iommu_ctrs(struct zpci_dev *zdev)
>  {
>  	if (!zdev || !zdev->s390_domain)
> @@ -785,7 +780,6 @@ static const struct iommu_ops s390_iommu_ops = {
>  	.capable = s390_iommu_capable,
>  	.domain_alloc_paging = s390_domain_alloc_paging,
>  	.probe_device = s390_iommu_probe_device,
> -	.probe_finalize = s390_iommu_probe_finalize,
>  	.release_device = s390_iommu_release_device,
>  	.device_group = generic_device_group,
>  	.pgsize_bitmap = SZ_4K,

I gave this whole series a test boot on s390 and also tried running a
KVM guest with vfio-pci pass-through. For the s390 part feel free to
add my.

Acked-by: Niklas Schnelle <schnelle@...ux.ibm.com> # for s390
Tested-by: Niklas Schnelle <schnelle@...ux.ibm.com> # for s390

Thanks,
Niklas