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:

quoted

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/ (local)
[3]
https://lore.kernel.org/linux-iommu/20200626002710.110200-2-rajatja@google.com/ (local)

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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