ACPI: Disable the C2C3_FFH access mode HW has no MWAIT support

991528d7348667924176f3e29addea0675298944
(ACPI: Processor native C-states using MWAIT)
started passing C2C3_FFH to _PDC to tell the BIOS
that Linux supports MWAIT for deep C-states.

However, we should first double check with the hardware
that it actually supports MWAIT before potentially exposing
a BIOS bug of an MWAIT _CST on HW that doesn't support MWAIT.

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Li Shaohua <shaohua.li@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

arch/x86/kernel/acpi/processor.c

@@ -56,6 +56,12 @@ static void init_intel_pdc(struct acpi_processor *pr, struct cpuinfo_x86 *c)
 	if (cpu_has(c, X86_FEATURE_ACPI))
 		buf[2] |= ACPI_PDC_T_FFH;
 
+	/*
+	 * If mwait/monitor is unsupported, C2/C3_FFH will be disabled
+	 */
+	if (!cpu_has(c, X86_FEATURE_MWAIT))
+		buf[2] &= ~(ACPI_PDC_C_C2C3_FFH);
+
 	obj->type = ACPI_TYPE_BUFFER;
 	obj->buffer.length = 12;
 	obj->buffer.pointer = (u8 *) buf;