linux-kernel - RE: [PATCH v4 2/6] iommu: Add a helper to do PASID lookup from domain

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Date:   Mon, 23 May 2022 07:55:01 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        "Lu Baolu" <baolu.lu@...ux.intel.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "will@...nel.org" <will@...nel.org>
CC:     "Liu, Yi L" <yi.l.liu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Eric Auger <eric.auger@...hat.com>
Subject: RE: [PATCH v4 2/6] iommu: Add a helper to do PASID lookup from domain

> From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Sent: Thursday, May 19, 2022 2:21 AM
> 
> IOMMU group maintains a PASID array which stores the associated IOMMU
> domains. This patch introduces a helper function to do domain to PASID
> look up. It will be used by TLB flush and device-PASID attach verification.
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> ---
>  drivers/iommu/iommu.c | 22 ++++++++++++++++++++++
>  include/linux/iommu.h |  6 +++++-
>  2 files changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 00d0262a1fe9..22f44833db64 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -3199,3 +3199,25 @@ struct iommu_domain
> *iommu_get_domain_for_iopf(struct device *dev,
> 
>  	return domain;
>  }
> +
> +ioasid_t iommu_get_pasid_from_domain(struct device *dev, struct
> iommu_domain *domain)
> +{
> +	struct iommu_domain *tdomain;
> +	struct iommu_group *group;
> +	unsigned long index;
> +	ioasid_t pasid = INVALID_IOASID;
> +
> +	group = iommu_group_get(dev);
> +	if (!group)
> +		return pasid;
> +
> +	xa_for_each(&group->pasid_array, index, tdomain) {
> +		if (domain == tdomain) {
> +			pasid = index;
> +			break;
> +		}
> +	}

Don't we need to acquire the group lock here?

Btw the intention of this function is a bit confusing. Patch01 already
stores the pasid under domain hence it's redundant to get it 
indirectly from xarray index. You could simply introduce a flag bit
(e.g. dma_pasid_enabled) in device_domain_info and then directly
use domain->dma_pasid once the flag is true.

> +	iommu_group_put(group);
> +
> +	return pasid;
> +}
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 36ad007084cc..c0440a4be699 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -694,7 +694,7 @@ void iommu_detach_device_pasid(struct
> iommu_domain *domain,
>  			       struct device *dev, ioasid_t pasid);
>  struct iommu_domain *
>  iommu_get_domain_for_iopf(struct device *dev, ioasid_t pasid);
> -
> +ioasid_t iommu_get_pasid_from_domain(struct device *dev, struct
> iommu_domain *domain);
>  #else /* CONFIG_IOMMU_API */
> 
>  struct iommu_ops {};
> @@ -1070,6 +1070,10 @@ iommu_get_domain_for_iopf(struct device *dev,
> ioasid_t pasid)
>  {
>  	return NULL;
>  }
> +static ioasid_t iommu_get_pasid_from_domain(struct device *dev, struct
> iommu_domain *domain)
> +{
> +	return INVALID_IOASID;
> +}
>  #endif /* CONFIG_IOMMU_API */
> 
>  #ifdef CONFIG_IOMMU_SVA
> --
> 2.25.1