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a881b49694
The VFIO_DEVICE_GET_INFO, VFIO_DEVICE_GET_REGION_INFO, and VFIO_IOMMU_GET_INFO ioctls fill in an info struct followed by capability structs: +------+---------+---------+-----+ | info | caps[0] | caps[1] | ... | +------+---------+---------+-----+ Both the info and capability struct sizes are not always multiples of sizeof(u64), leaving u64 fields in later capability structs misaligned. Userspace applications currently need to handle misalignment manually in order to support CPU architectures and programming languages with strict alignment requirements. Make life easier for userspace by ensuring alignment in the kernel. This is done by padding info struct definitions and by copying out zeroes after capability structs that are not aligned. The new layout is as follows: +------+---------+---+---------+-----+ | info | caps[0] | 0 | caps[1] | ... | +------+---------+---+---------+-----+ In this example caps[0] has a size that is not multiples of sizeof(u64), so zero padding is added to align the subsequent structure. Adding zero padding between structs does not break the uapi. The memory layout is specified by the info.cap_offset and caps[i].next fields filled in by the kernel. Applications use these field values to locate structs and are therefore unaffected by the addition of zero padding. Note that code that copies out info structs with padding is updated to always zero the struct and copy out as many bytes as userspace requested. This makes the code shorter and avoids potential information leaks by ensuring padding is initialized. Originally-by: Alex Williamson <alex.williamson@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Kevin Tian <kevin.tian@intel.com> Acked-by: Jason Gunthorpe <jgg@nvidia.com> Link: https://lore.kernel.org/r/20230809203144.2880050-1-stefanha@redhat.com Signed-off-by: Alex Williamson <alex.williamson@redhat.com> |
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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.