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Date:   Wed, 1 Apr 2020 15:58:48 +0200
From:   Jean-Philippe Brucker <jean-philippe@linaro.org>
To:     Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc:     Joerg Roedel <joro@8bytes.org>,
        Alex Williamson <alex.williamson@redhat.com>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        iommu@lists.linux-foundation.org,
        LKML <linux-kernel@vger.kernel.org>,
        David Woodhouse <dwmw2@infradead.org>,
        Jean-Philippe Brucker <jean-philippe@linaro.com>,
        Yi Liu <yi.l.liu@intel.com>,
        "Tian, Kevin" <kevin.tian@intel.com>,
        Raj Ashok <ashok.raj@intel.com>,
        Christoph Hellwig <hch@infradead.org>,
        Jonathan Cameron <jic23@kernel.org>,
        Eric Auger <eric.auger@redhat.com>
Subject: Re: [PATCH 07/10] iommu/ioasid: Use mutex instead of spinlock
Message-ID: <20200401135848.GH882512@myrica>
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 <1585158931-1825-8-git-send-email-jacob.jun.pan@linux.intel.com>
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On Wed, Mar 25, 2020 at 10:55:28AM -0700, Jacob Pan wrote:
> Each IOASID or set could have multiple users with its own HW context
> to maintain. Often times access to the HW context requires thread context.
> For example, consumers of IOASIDs can register notification blocks to
> sync up its states. Having an atomic notifier is not feasible for these
> update operations.
> 
> This patch converts allocator lock from spinlock to mutex in preparation
> for IOASID notifier.

Unfortunately this doesn't work for SVA, which needs to call ioasid_free()
from the RCU callback of mmu_notifier_put(), which cannot sleep. We're
relying on MMU notifers this way to ensure that there is a single IOASID
per mm.

Thanks,
Jean