platform/x86/intel/ifs: Add stub driver for In-Field Scan

Cloud Service Providers that operate fleets of servers have reported
[1] occasions where they can detect that a CPU has gone bad due to
effects like electromigration, or isolated manufacturing defects.
However, that detection method is A/B testing seemingly random
application failures looking for a pattern. In-Field Scan (IFS) is
a driver for a platform capability to load a crafted 'scan image'
to run targeted low level diagnostics outside of the CPU's architectural
error detection capabilities.

Stub version of driver just does initial part of check for the IFS
feature. MSR_IA32_CORE_CAPS must enumerate the presence of the
MSR_INTEGRITY_CAPS MSR.

[1]: https://www.youtube.com/watch?v=QMF3rqhjYuM

Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20220506225410.1652287-5-tony.luck@intel.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

MAINTAINERS

@@ -9859,6 +9859,13 @@ B:	https://bugzilla.kernel.org
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux.git
 F:	drivers/idle/intel_idle.c
 
+INTEL IN FIELD SCAN (IFS) DEVICE
+M:	Jithu Joseph <jithu.joseph@intel.com>
+R:	Ashok Raj <ashok.raj@intel.com>
+R:	Tony Luck <tony.luck@intel.com>
+S:	Maintained
+F:	drivers/platform/x86/intel/ifs
+
 INTEL INTEGRATED SENSOR HUB DRIVER
 M:	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
 M:	Jiri Kosina <jikos@kernel.org>

drivers/platform/x86/intel/Kconfig

@@ -4,6 +4,7 @@
 #
 
 source "drivers/platform/x86/intel/atomisp2/Kconfig"
+source "drivers/platform/x86/intel/ifs/Kconfig"
 source "drivers/platform/x86/intel/int1092/Kconfig"
 source "drivers/platform/x86/intel/int3472/Kconfig"
 source "drivers/platform/x86/intel/pmc/Kconfig"

drivers/platform/x86/intel/Makefile

@@ -5,6 +5,7 @@
 #
 
 obj-$(CONFIG_INTEL_ATOMISP2_PDX86)	+= atomisp2/
+obj-$(CONFIG_INTEL_IFS)			+= ifs/
 obj-$(CONFIG_INTEL_SAR_INT1092)		+= int1092/
 obj-$(CONFIG_INTEL_SKL_INT3472)		+= int3472/
 obj-$(CONFIG_INTEL_PMC_CORE)		+= pmc/

drivers/platform/x86/intel/ifs/Kconfig

@@ -0,0 +1,13 @@
+config INTEL_IFS
+	tristate "Intel In Field Scan"
+	depends on X86 && 64BIT && SMP
+	select INTEL_IFS_DEVICE
+	help
+	  Enable support for the In Field Scan capability in select
+	  CPUs. The capability allows for running low level tests via
+	  a scan image distributed by Intel via Github to validate CPU
+	  operation beyond baseline RAS capabilities. To compile this
+	  support as a module, choose M here. The module will be called
+	  intel_ifs.
+
+	  If unsure, say N.

drivers/platform/x86/intel/ifs/Makefile

@@ -0,0 +1,3 @@
+obj-$(CONFIG_INTEL_IFS)		+= intel_ifs.o
+
+intel_ifs-objs			:= core.o

drivers/platform/x86/intel/ifs/core.c

@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright(c) 2022 Intel Corporation. */
+
+#include <linux/module.h>
+#include <linux/kdev_t.h>
+
+#include <asm/cpu_device_id.h>
+
+#define X86_MATCH(model)				\
+	X86_MATCH_VENDOR_FAM_MODEL_FEATURE(INTEL, 6,	\
+		INTEL_FAM6_##model, X86_FEATURE_CORE_CAPABILITIES, NULL)
+
+static const struct x86_cpu_id ifs_cpu_ids[] __initconst = {
+	X86_MATCH(SAPPHIRERAPIDS_X),
+	{}
+};
+MODULE_DEVICE_TABLE(x86cpu, ifs_cpu_ids);
+
+static int __init ifs_init(void)
+{
+	const struct x86_cpu_id *m;
+	u64 msrval;
+
+	m = x86_match_cpu(ifs_cpu_ids);
+	if (!m)
+		return -ENODEV;
+
+	if (rdmsrl_safe(MSR_IA32_CORE_CAPS, &msrval))
+		return -ENODEV;
+
+	if (!(msrval & MSR_IA32_CORE_CAPS_INTEGRITY_CAPS))
+		return -ENODEV;
+
+	if (rdmsrl_safe(MSR_INTEGRITY_CAPS, &msrval))
+		return -ENODEV;
+
+	return 0;
+}
+
+static void __exit ifs_exit(void)
+{
+}
+
+module_init(ifs_init);
+module_exit(ifs_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Intel In Field Scan (IFS) device");