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When running on an AMD vIOMMU, it is better to avoid TLB flushes of unmodified PTEs. vIOMMUs require the hypervisor to synchronize the virtualized IOMMU's PTEs with the physical ones. This process induce overheads. AMD IOMMU allows us to flush any range that is aligned to the power of 2. So when running on top of a vIOMMU, break the range into sub-ranges that are naturally aligned, and flush each one separately. This apporach is better when running with a vIOMMU, but on physical IOMMUs, the penalty of IOTLB misses due to unnecessary flushed entries is likely to be low. Repurpose (i.e., keeping the name, changing the logic) domain_flush_pages() so it is used to choose whether to perform one flush of the whole range or multiple ones to avoid flushing unnecessary ranges. Use NpCache, as usual, to infer whether the IOMMU is physical or virtual. Cc: Joerg Roedel <joro@8bytes.org> Cc: Will Deacon <will@kernel.org> Cc: Jiajun Cao <caojiajun@vmware.com> Cc: Lu Baolu <baolu.lu@linux.intel.com> Cc: iommu@lists.linux-foundation.org Cc: linux-kernel@vger.kernel.org Suggested-by: Robin Murphy <robin.murphy@arm.com> Signed-off-by: Nadav Amit <namit@vmware.com> Link: https://lore.kernel.org/r/20210723093209.714328-8-namit@vmware.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.