x86/reboot: KVM: Handle VMXOFF in KVM's reboot callback

x86/reboot: KVM: Handle VMXOFF in KVM's reboot callback

[ Upstream commit 119b5cb4ffd0166f3e98e9ee042f5046f7744f28 ]

Use KVM VMX's reboot/crash callback to do VMXOFF in an emergency instead
of manually and blindly doing VMXOFF.  There's no need to attempt VMXOFF
if a hypervisor, i.e. KVM, isn't loaded/active, i.e. if the CPU can't
possibly be post-VMXON.

Reviewed-by: Kai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/r/20230721201859.2307736-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Stable-dep-of: a0ee1d5faff1 ("KVM: VMX: Flush shadow VMCS on emergency reboot")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>