5ab2f45bba
KVM can request fpstate expansion in two approaches: 1) When intercepting guest updates to XCR0 and XFD MSR; 2) Before vcpu runs (e.g. at KVM_SET_CPUID2); The first option doesn't waste memory for legacy guest if it doesn't support XFD. However doing so introduces more complexity and also imposes an order requirement in the restoring path, i.e. XCR0/XFD must be restored before XSTATE. Given that the agreement is to do the static approach. This is considered a better tradeoff though it does waste 8K memory for legacy guest if its CPUID includes dynamically-enabled xfeatures. Successful fpstate expansion requires userspace VMM to acquire guest xstate permissions before calling KVM_SET_CPUID2. Also take the chance to adjust the indent in kvm_set_cpuid(). Signed-off-by: Jing Liu <jing2.liu@intel.com> Signed-off-by: Sean Christopherson <seanjc@google.com> Signed-off-by: Kevin Tian <kevin.tian@intel.com> Signed-off-by: Yang Zhong <yang.zhong@intel.com> Message-Id: <20220105123532.12586-9-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.