linux-kernel - Re: [PATCH v2 22/24] iommu: Allow enabling non-strict mode dynamically

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Date:   Fri, 30 Jul 2021 10:24:24 +0100
From:   John Garry <john.garry@...wei.com>
To:     Robin Murphy <robin.murphy@....com>, <joro@...tes.org>,
        <will@...nel.org>
CC:     <iommu@...ts.linux-foundation.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <suravee.suthikulpanit@....com>,
        <baolu.lu@...ux.intel.com>, <dianders@...omium.org>
Subject: Re: [PATCH v2 22/24] iommu: Allow enabling non-strict mode
 dynamically

On 28/07/2021 16:58, Robin Murphy wrote:
> Allocating and enabling a flush queue is in fact something we can
> reasonably do while a DMA domain is active, without having to rebuild it
> from scratch. Thus we can allow a strict -> non-strict transition from
> sysfs without requiring to unbind the device's driver, which is of
> particular interest to users who want to make selective relaxations to
> critical devices like the one serving their root filesystem.
> 
> Disabling and draining a queue also seems technically possible to
> achieve without rebuilding the whole domain, but would certainly be more
> involved. Furthermore there's not such a clear use-case for tightening
> up security*after*  the device may already have done whatever it is that
> you don't trust it not to do, so we only consider the relaxation case.
> 
> Signed-off-by: Robin Murphy<robin.murphy@....com>

Reviewed-by: John Garry <john.garry@...wei.com>