linux-kernel - Re: [PATCH 08/10] iommu/ioasid: Introduce notifier APIs

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Message-ID: <20200401140006.GI882512@myrica>
Date:   Wed, 1 Apr 2020 16:00:06 +0200
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Eric Auger <eric.auger@...hat.com>
Subject: Re: [PATCH 08/10] iommu/ioasid: Introduce notifier APIs

On Wed, Mar 25, 2020 at 10:55:29AM -0700, Jacob Pan wrote:
> IOASID users fit into the publisher-subscriber pattern, a system wide
> blocking notifier chain can be used to inform subscribers of state
> changes. Notifier mechanism also abstracts publisher from knowing the
> private context each subcriber may have.
> 
> This patch adds APIs and a global notifier chain, a further optimization
> might be per set notifier for ioasid_set aware users.
> 
> Usage example:
> KVM register notifier block such that it can keep its guest-host PASID
> translation table in sync with any IOASID updates.

When you talk about KVM, is it for

  [PATCH 0/7] x86: tag application address space for devices

or something else as well? (I don't see mentions of KVM in that series)

> 
> VFIO publish IOASID change by performing alloc/free, bind/unbind
> operations.

I was rather seeing IOASID as the end of the VFIO-IOMMU-IOASID chain,
putting it in the middle complicates locking. If you only need to FREE
notifier for this calse, maybe VFIO could talk directly to the IOMMU
driver before freeing an IOASID?  gpasid_unbind() should already clear the
PASID contexts, no?

Thanks,
Jean

> IOMMU driver gets notified when IOASID is freed by VFIO or core mm code
> such that PASID context can be cleaned up.
> 
> Signed-off-by: Liu Yi L <yi.l.liu@...el.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>