linux-kernel - Re: [PATCH 3/4] iommu/vt-d: Support PASID DMA for in-kernel usage

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Date:   Wed, 8 Dec 2021 09:22:55 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Jacob Pan <jacob.jun.pan@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Raj Ashok <ashok.raj@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Tony Luck <tony.luck@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Barry Song <21cnbao@...il.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH 3/4] iommu/vt-d: Support PASID DMA for in-kernel usage

On Tue, Dec 07, 2021 at 05:47:13AM -0800, Jacob Pan wrote:
> Between DMA requests with and without PASID (legacy), DMA mapping APIs
> are used indiscriminately on a device. Therefore, we should always match
> the addressing mode of the legacy DMA when enabling kernel PASID.
> 
> This patch adds support for VT-d driver where the kernel PASID is
> programmed to match RIDPASID. i.e. if the device is in pass-through, the
> kernel PASID is also in pass-through; if the device is in IOVA mode, the
> kernel PASID will also be using the same IOVA space.
> 
> There is additional handling for IOTLB and device TLB flush w.r.t. the
> kernel PASID. On VT-d, PASID-selective IOTLB flush is also on a
> per-domain basis; whereas device TLB flush is per device. Note that
> IOTLBs are used even when devices are in pass-through mode. ATS is
> enabled device-wide, but the device drivers can choose to manage ATS at
> per PASID level whenever control is available.
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
>  drivers/iommu/intel/iommu.c | 105 +++++++++++++++++++++++++++++++++++-
>  drivers/iommu/intel/pasid.c |   7 +++
>  include/linux/intel-iommu.h |   3 +-
>  3 files changed, 113 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 60253bc436bb..a2ef6b9e4bfc 100644
> +++ b/drivers/iommu/intel/iommu.c
> @@ -1743,7 +1743,14 @@ static void domain_flush_piotlb(struct intel_iommu *iommu,
>  	if (domain->default_pasid)
>  		qi_flush_piotlb(iommu, did, domain->default_pasid,
>  				addr, npages, ih);
> -
> +	if (domain->kernel_pasid && !domain_type_is_si(domain)) {
> +		/*
> +		 * REVISIT: we only do PASID IOTLB inval for FL, we could have SL
> +		 * for PASID in the future such as vIOMMU PT. this doesn't get hit.
> +		 */
> +		qi_flush_piotlb(iommu, did, domain->kernel_pasid,
> +				addr, npages, ih);
> +	}
>  	if (!list_empty(&domain->devices))
>  		qi_flush_piotlb(iommu, did, PASID_RID2PASID, addr, npages, ih);
>  }
> @@ -5695,6 +5702,100 @@ static void intel_iommu_iotlb_sync_map(struct iommu_domain *domain,
>  	}
>  }
>  
> +static int intel_enable_pasid_dma(struct device *dev, u32 pasid)
> +{

This seems like completely the wrong kind of op.

At the level of the iommu driver things should be iommu_domain centric

The op should be

int attach_dev_pasid(struct iommu_domain *domain, struct device *dev, ioasid_t pasid)

Where 'dev' purpose is to provide the RID

The iommu_domain passed in should be the 'default domain' ie the table
used for on-demand mapping, or the passthrough page table.

> +	struct intel_iommu *iommu = device_to_iommu(dev, NULL, NULL);
> +	struct device_domain_info *info;

I don't even want to know why an iommu driver is tracking its own
per-device state. That seems like completely wrong layering.

Jason