linux-kernel - Re: [PATCH v8 01/11] iommu: Add max_pasids field in struct iommu

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Message-ID: <20220609235303.GC1343366@nvidia.com>
Date:   Thu, 9 Jun 2022 20:53:03 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Raj, Ashok" <ashok.raj@...el.com>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: Re: [PATCH v8 01/11] iommu: Add max_pasids field in struct
 iommu_device

On Thu, Jun 09, 2022 at 05:25:42PM +0000, Raj, Ashok wrote:
> 
> On Tue, Jun 07, 2022 at 09:49:32AM +0800, Lu Baolu wrote:
> > Use this field to keep the number of supported PASIDs that an IOMMU
> > hardware is able to support. This is a generic attribute of an IOMMU
> > and lifting it into the per-IOMMU device structure makes it possible
> 
> There is also a per-device attribute that tells what width is supported on
> each device. When a device enables SVM, for simplicity we were proposing to
> disable SVM on devices that don't support the full width, since it adds
> additional complexity on the allocation interface. Is that factored into
> this?

I would like to see the concept of a 'global PASID' and this is the
only place we'd union all the per-device limits together. SVM can
optionally use a global PASID and ENQCMD requires it, but I don't want
to see the core code assuming everything is ENQCMD.

Jason