x86/hvm: Don't raise #GP behind the emulators back for MSR accesses

x86/hvm: Don't raise #GP behind the emulators back for MSR accesses

The current hvm_msr_{read,write}_intercept() infrastructure calls
hvm_inject_hw_exception() directly to latch a fault, and returns
X86EMUL_EXCEPTION to its caller.

This behaviour is problematic for the hvmemul_{read,write}_msr() paths, as the
fault is raised behind the back of the x86 emulator.

Alter the behaviour so hvm_msr_{read,write}_intercept() simply returns
X86EMUL_EXCEPTION, leaving the callers to actually inject the #GP fault.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>