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8cc633190b
Although strictly it is the AMD and Intel drivers which have an existing expectation of lazy behaviour by default, it ends up being rather unintuitive to describe this literally in Kconfig. Express it instead as an architecture dependency, to clarify that it is a valid config-time decision. The end result is the same since virtio-iommu doesn't support lazy mode and thus falls back to strict at runtime regardless. The per-architecture disparity is a matter of historical expectations: the AMD and Intel drivers have been lazy by default since 2008, and changing that gets noticed by people asking where their I/O throughput has gone. Conversely, Arm-based systems with their wider assortment of IOMMU drivers mostly only support strict mode anyway; only the Arm SMMU drivers have later grown support for passthrough and lazy mode, for users who wanted to explicitly trade off isolation for performance. These days, reducing the default level of isolation in a way which may go unnoticed by users who expect otherwise hardly seems worth risking for the sake of one line of Kconfig, so here's where we are. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Robin Murphy <robin.murphy@arm.com> Link: https://lore.kernel.org/r/69a0c6f17b000b54b8333ee42b3124c1d5a869e2.1631105737.git.robin.murphy@arm.com Signed-off-by: Joerg Roedel <jroedel@suse.de>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.