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WARN if CR0, CR3, or CR4 are non-zero at RESET, which given the current KVM implementation, really means WARN if they're not zeroed at vCPU creation. VMX in particular has several ->set_*() flows that read other registers to handle side effects, and because those flows are common to RESET and INIT, KVM subtly relies on emulated/virtualized registers to be zeroed at vCPU creation in order to do the right thing at RESET. Use CRs as a sentinel because they are most likely to be written as side effects, and because KVM specifically needs CR0.PG and CR0.PE to be '0' to correctly reflect the state of the vCPU's MMU. CRs are also loaded and stored from/to the VMCS, and so adds some level of coverage to verify that KVM doesn't conflate zero-allocating the VMCS with properly initializing the VMCS with VMWRITEs. Note, '0' is somewhat arbitrary, vCPU creation can technically stuff any value for a register so long as it's coherent with respect to the current vCPU state. In practice, '0' works for all registers and is convenient. Suggested-by: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: Sean Christopherson <seanjc@google.com> Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-Id: <20210921000303.400537-11-seanjc@google.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.