KVM x86 fixes and a selftest fix for 6.17-rcN
- Use array_index_nospec() to sanitize the target vCPU ID when handling PV
IPIs and yields as the ID is guest-controlled.
- Drop a superfluous cpumask_empty() check when reclaiming SEV memory, as
the common case, by far, is that at least one CPU will have entered the
VM, and wbnoinvd_on_cpus_mask() will naturally handle the rare case where
the set of have_run_cpus is empty.
- Rename the is_signed_type() macro in kselftest_harness.h to is_signed_var()
to fix a collision with linux/overflow.h. The collision generates compiler
warnings due to the two macros having different implementations.