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XSK RQs support striding RQ linear mode, but the stride size may be bigger than the XSK frame size, because: 1. The stride size must be a power of two. 2. The stride size must be equal to the UMR page size. Each XSK frame is treated as a separate page, because they aren't necessarily adjacent in physical memory, so the driver can't put more than one stride per page. 3. The minimal MTT page size is 4096 on older firmware. That means that if XSK frame size is 2048 or not a power of two, the strides may be bigger than XSK frames. Normally, it's not a problem if the hardware enforces the MTU. However, traffic between vports skips the hardware MTU check, and oversized packets may be received. If an oversized packet is bigger than the XSK frame but not bigger than the stride, it will cause overwriting of the adjacent UMEM region. If the packet takes more than one stride, they can be recycled for reuse, so it's not a problem when the XSK frame size matches the stride size. Work around the above issue by leveraging KLM to make a more fine-grained mapping. The beginning of each stride is mapped to the frame memory, and the padding up to the closest power of two is mapped to the overflow page that doesn't belong to UMEM. This way, application data corruption won't happen upon receiving packets bigger than MTU. Signed-off-by: Maxim Mikityanskiy <maximmi@nvidia.com> Reviewed-by: Tariq Toukan <tariqt@nvidia.com> Signed-off-by: Saeed Mahameed <saeedm@nvidia.com> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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.