914eedcb9b
The basic interaction for setting up a userfaultfd is, userspace issues a UFFDIO_API ioctl, and passes in a set of zero or more feature flags, indicating the features they would prefer to use. Of course, different kernels may support different sets of features (depending on kernel version, kconfig options, architecture, etc). Userspace's expectations may also not match: perhaps it was built against newer kernel headers, which defined some features the kernel it's running on doesn't support. Currently, if userspace passes in a flag we don't recognize, the initialization fails and we return -EINVAL. This isn't great, though. Userspace doesn't have an obvious way to react to this; sure, one of the features I asked for was unavailable, but which one? The only option it has is to turn off things "at random" and hope something works. Instead, modify UFFDIO_API to just ignore any unrecognized feature flags. The interaction is now that the initialization will succeed, and as always we return the *subset* of feature flags that can actually be used back to userspace. Now userspace has an obvious way to react: it checks if any flags it asked for are missing. If so, it can conclude this kernel doesn't support those, and it can either resign itself to not using them, or fail with an error on its own, or whatever else. Link: https://lkml.kernel.org/r/20220722201513.1624158-1-axelrasmussen@google.com Signed-off-by: Axel Rasmussen <axelrasmussen@google.com> Cc: Peter Xu <peterx@redhat.com> Cc: Axel Rasmussen <axelrasmussen@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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| Documentation | ||
| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
README
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.