linux-kernel - Re: [PATCH 07/10] iommu/ioasid: Use mutex instead of spinlock

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Message-ID: <20200401135848.GH882512@myrica>
Date:   Wed, 1 Apr 2020 15:58:48 +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 07/10] iommu/ioasid: Use mutex instead of spinlock

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