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3243b93c16
Advertise UMIP as emulated if and only if the host doesn't natively support UMIP, otherwise vmx_umip_emulated() is misleading when the host _does_ support UMIP. Of the four users of vmx_umip_emulated(), two already check for native support, and the logic in vmx_set_cpu_caps() is relevant if and only if UMIP isn't natively supported as UMIP is set in KVM's caps by kvm_set_cpu_caps() when UMIP is present in hardware. That leaves KVM's stuffing of X86_CR4_UMIP into the default cr4_fixed1 value enumerated for nested VMX. In that case, checking for (lack of) host support is actually a bug fix of sorts, as enumerating UMIP support based solely on descriptor table exiting works only because KVM doesn't sanity check MSR_IA32_VMX_CR4_FIXED1. E.g. if a (very theoretical) host supported UMIP in hardware but didn't allow UMIP+VMX, KVM would advertise UMIP but not actually emulate UMIP. Of course, KVM would explode long before it could run a nested VM on said theoretical CPU, as KVM doesn't modify host CR4 when enabling VMX, i.e. would load an "illegal" value into vmcs.HOST_CR4. Reported-by: Robert Hoo <robert.hu@intel.com> Link: https://lore.kernel.org/all/20230310125718.1442088-2-robert.hu@intel.com Link: https://lore.kernel.org/r/20230413231914.1482782-2-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.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.