mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-05-07 18:37:58 -04:00
cf81a7e580
Linux does not support Memory Protection Extensions (MPX) in the kernel itself, thus the BNDCFGS (Bound Config Supervisor) MSR will always be zero in the KVM host, i.e. RDMSR in vmx_save_host_state() is superfluous. KVM unconditionally sets VM_EXIT_CLEAR_BNDCFGS, i.e. BNDCFGS will always be zero after VMEXIT, thus manually loading BNDCFGS is also superfluous. And in the event the MPX kernel support is added (unlikely given that MPX for userspace is in its death throes[1]), BNDCFGS will likely be common across all CPUs[2], and at the least shouldn't change on a regular basis, i.e. saving the MSR on every VMENTRY is completely unnecessary. WARN_ONCE in hardware_setup() if the host's BNDCFGS is non-zero to document that KVM does not preserve BNDCFGS and to serve as a hint as to how BNDCFGS likely should be handled if MPX is used in the kernel, e.g. BNDCFGS should be saved once during KVM setup. [1] https://lkml.org/lkml/2018/4/27/1046 [2] http://www.openwall.com/lists/kernel-hardening/2017/07/24/28 Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.