84361529ee
Tigerlake is plagued by spontaneous DMAR faults [reason 7, next page table ptr is invalid] which lead to GPU hangs. These faults occur when an iommu map is immediately reused. Adding further clflushes and barriers around either the GTT PTE or iommu PTE updates do not prevent the faults. So far the only effect has been from inducing a delay between reuse of the iommu on the GPU, and applying the delay at the iommu map allows for the smallest stable delay. Note that such a delay is hideous and clearly does not fix the root cause, and so should only be a bandaid until a complete solution is found. The delay was determined by running igt/gem_exec_fence/parallel in a loop for a few hours (unpatched MTBF is about 10s). We have also seen such DMAR fault [reason 7] errors on other platforms, notably gen9-gen11, but so far it has only been trivially and consistently reproduced on Tigerlake. v2: Leave a tell-tale to know when we apply the vt'd quirk, and as a reminder to remove it again. Hopefully. Testcase: igt/gem_exec_fence/parallel Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com> Acked-by: Mika Kuoppala <mika.kuoppala@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20201209164008.5487-2-chris@chris-wilson.co.uk
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.