x86/vmx: Introduce VMX_FEATURES_*

Add a VMX-specific variant of X86_FEATURE_* flags, which will eventually
supplant the synthetic VMX flags defined in cpufeatures word 8.  Use the
Intel-defined layouts for the major VMX execution controls so that their
word entries can be directly populated from their respective MSRs, and
so that the VMX_FEATURE_* flags can be used to define the existing bit
definitions in asm/vmx.h, i.e. force developers to define a VMX_FEATURE
flag when adding support for a new hardware feature.

The majority of Intel's (and compatible CPU's) VMX capabilities are
enumerated via MSRs and not CPUID, i.e. querying /proc/cpuinfo doesn't
naturally provide any insight into the virtualization capabilities of
VMX enabled CPUs.  Commit

  e38e05a8 ("x86: extended "flags" to show virtualization HW feature
		 in /proc/cpuinfo")

attempted to address the issue by synthesizing select VMX features into
a Linux-defined word in cpufeatures.

Lack of reporting of VMX capabilities via /proc/cpuinfo is problematic
because there is no sane way for a user to query the capabilities of
their platform, e.g. when trying to find a platform to test a feature or
debug an issue that has a hardware dependency.  Lack of reporting is
especially problematic when the user isn't familiar with VMX, e.g. the
format of the MSRs is non-standard, existence of some MSRs is reported
by bits in other MSRs, several "features" from KVM's point of view are
enumerated as 3+ distinct features by hardware, etc...

The synthetic cpufeatures approach has several flaws:

  - The set of synthesized VMX flags has become extremely stale with
    respect to the full set of VMX features, e.g. only one new flag
    (EPT A/D) has been added in the the decade since the introduction of
    the synthetic VMX features.  Failure to keep the VMX flags up to
    date is likely due to the lack of a mechanism that forces developers
    to consider whether or not a new feature is worth reporting.

  - The synthetic flags may incorrectly be misinterpreted as affecting
    kernel behavior, i.e. KVM, the kernel's sole consumer of VMX,
    completely ignores the synthetic flags.

  - New CPU vendors that support VMX have duplicated the hideous code
    that propagates VMX features from MSRs to cpufeatures.  Bringing the
    synthetic VMX flags up to date would exacerbate the copy+paste
    trainwreck.

Define separate VMX_FEATURE flags to set the stage for enumerating VMX
capabilities outside of the cpu_has() framework, and for adding
functional usage of VMX_FEATURE_* to help ensure the features reported
via /proc/cpuinfo is up to date with respect to kernel recognition of
VMX capabilities.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20191221044513.21680-10-sean.j.christopherson@intel.com