linux-kernel - Re: [PATCH] iommu: Add support to filter non-strict/lazy mode based on device names

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Date:   Wed, 26 Aug 2020 17:47:30 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Robin Murphy <robin.murphy@....com>,
        Douglas Anderson <dianders@...omium.org>
Cc:     Will Deacon <will@...nel.org>, Joerg Roedel <joro@...tes.org>,
        Tomasz Figa <tfiga@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] iommu: Add support to filter non-strict/lazy mode based
 on device names

On 2020-08-26 17:07, Robin Murphy wrote:
> On 2020-08-25 16:42, Sai Prakash Ranjan wrote:
>> Currently the non-strict or lazy mode of TLB invalidation can only be 
>> set
>> for all or no domains. This works well for development platforms where
>> setting to non-strict/lazy mode is fine for performance reasons but on
>> production devices, we need a more fine grained control to allow only
>> certain peripherals to support this mode where we can be sure that it 
>> is
>> safe. So add support to filter non-strict/lazy mode based on the 
>> device
>> names that are passed via cmdline parameter "iommu.nonstrict_device".
> 
> There seems to be considerable overlap here with both the existing
> patches for per-device default domain control [1], and the broader
> ongoing development on how to define, evaluate and handle "trusted"
> vs. "untrusted" devices (e.g. [2],[3]). I'd rather see work done to
> make sure those integrate properly together and work well for
> everyone's purposes, than add more disjoint mechanisms that only
> address small pieces of the overall issue.
> 
> Robin.
> 
> [1]
> https://lore.kernel.org/linux-iommu/20200824051726.7xaJRTTszJuzdFWGJ8YNsshCtfNR0BNeMrlILAyqt_0@z/
> [2]
> https://lore.kernel.org/linux-iommu/20200630044943.3425049-1-rajatja@google.com/
> [3]
> https://lore.kernel.org/linux-iommu/20200626002710.110200-2-rajatja@google.com/
> 

Thanks for the links, [1] definitely sounds interesting, I was under the 
impression
that changing such via sysfs is late, but seems like other Sai has got 
it working
for the default domain type. So we can extend that and add a strict 
attribute as well,
we should be definitely OK with system booting with default strict mode 
for all
peripherals as long as we have an option to change that later, Doug?

Thanks,
Sai

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