KVM: x86: allow RSM from 64-bit mode
KVM: x86: allow RSM from 64-bit mode

The SDM says that exiting system management mode from 64-bit mode
is invalid, but that would be too good to be true.  But actually,
most of the code is already there to support exiting from compat
mode (EFER.LME=1, EFER.LMA=0).  Getting all the way from 64-bit
mode to real mode only requires clearing CS.L and CR4.PCIDE.

Cc: 4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org
Fixes: 660a5d517aaab9187f93854425c4c63f4a09195c
Tested-by: Laszlo Ersek <7437296077edea1cb64451c122c4dac071f0cfbc@redhat.com>
Cc: Radim Krčmář <e4aea3f2c531804c57884e1d444a6744efb5af4d@redhat.com>
Signed-off-by: Paolo Bonzini <69d3ebcf5ee4e7f05a50dc23cd96655b730804b4@redhat.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs