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KVM can disable the write emulation for the XFD MSR when the vCPU's fpstate is already correctly sized to reduce the overhead. When write emulation is disabled the XFD MSR state after a VMEXIT is unknown and therefore not in sync with the software states in fpstate and the per CPU XFD cache. Provide fpu_sync_guest_vmexit_xfd_state() which has to be invoked after a VMEXIT before enabling interrupts when write emulation is disabled for the XFD MSR. It could be invoked unconditionally even when write emulation is enabled for the price of a pointless MSR read. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Jing Liu <jing2.liu@intel.com> Signed-off-by: Yang Zhong <yang.zhong@intel.com> Message-Id: <20220105123532.12586-21-yang.zhong@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.
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.
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