KVM: nVMX: Reference vmx->loaded_vmcs->launched directly

KVM: nVMX: Reference vmx->loaded_vmcs->launched directly

Temporarily propagating vmx->loaded_vmcs->launched to vmx->__launched
is not functionally necessary, but rather was done historically to
avoid passing both 'vmx' and 'loaded_vmcs' to the vCPU-run asm blob.
Nested early checks inherited this behavior by virtue of copy+paste.

A future patch will move HOST_RSP caching to be per-VMCS, i.e. store
'host_rsp' in loaded VMCS.  Now that the reference to 'vmx->fail' is
also gone from nested early checks, referencing 'loaded_vmcs' directly
means we can drop the 'vmx' reference when introducing per-VMCS RSP
caching.  And it means __launched can be dropped from struct vcpu_vmx
if/when vCPU-run receives similar treatment.

Note the use of a named register constraint for 'loaded_vmcs'.  Using
RCX to hold 'vmx' was inherited from vCPU-run.  In the vCPU-run case,
the scratch register needs to be explicitly defined as it is crushed
when loading guest state, i.e. deferring to the compiler would corrupt
the pointer.  Since nested early checks never loads guests state, it's
a-ok to let the compiler pick any register.  Naming the constraint
avoids the fragility of referencing constraints via %1, %2, etc.., which
breaks horribly when modifying constraints, and generally makes the asm
blob more readable.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>