x86/speculation/mmio: Enable CPU Fill buffer clearing on idle

x86/speculation/mmio: Enable CPU Fill buffer clearing on idle

commit 66dc70090df1b007df8d63bc809f4d1f39def0b0 upstream

When the CPU is affected by Processor MMIO Stale Data vulnerabilities,
Fill Buffer Stale Data Propagator (FBSDP) can propagate stale data out
of Fill buffer to uncore buffer when CPU goes idle. Stale data can then
be exploited with other variants using MMIO operations.

Mitigate it by clearing the Fill buffer before entering idle state.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Co-developed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>