linux-kernel - [PATCH 2/2] platform/x86/intel/ifs: Initialize AMX state for the scan test

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Date: Tue, 30 Apr 2024 14:25:08 -0700
From: "Chang S. Bae" <chang.seok.bae@...el.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org,
	platform-driver-x86@...r.kernel.org,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	hdegoede@...hat.com,
	ilpo.jarvinen@...ux.intel.com,
	tony.luck@...el.com,
	ashok.raj@...el.com,
	jithu.joseph@...el.com,
	chang.seok.bae@...el.com
Subject: [PATCH 2/2] platform/x86/intel/ifs: Initialize AMX state for the scan test

The scan test does not start when the AMX state remains active and is not
re-initialized. With the extension of kernel_fpu_begin_mask(), the driver
code can now initialize the state properly.

Introduce custom FPU handling wrappers to ensure compliant with the
established FPU API semantics, as kernel_fpu_begin() exclusively sets
legacy states. This follows the EFI case from commit b0dc553cfc9d
("x86/fpu: Make the EFI FPU calling convention explicit").

Then, use these wrappers to surround the MSR_ACTIVATE_SCAN write to
minimize the critical section. To prevent unnecessary delays, invoke
ifs_fpu_begin() before entering the rendezvous loop.

Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Reviewed-by: Jithu Joseph <jithu.joseph@...el.com>
Tested-by: Jithu Joseph <jithu.joseph@...el.com>
---
 drivers/platform/x86/intel/ifs/ifs.h     | 14 ++++++++++++++
 drivers/platform/x86/intel/ifs/runtest.c |  6 ++++++
 2 files changed, 20 insertions(+)

diff --git a/drivers/platform/x86/intel/ifs/ifs.h b/drivers/platform/x86/intel/ifs/ifs.h
index 56b9f3e3cf76..71d8b50854b2 100644
--- a/drivers/platform/x86/intel/ifs/ifs.h
+++ b/drivers/platform/x86/intel/ifs/ifs.h
@@ -325,4 +325,18 @@ int do_core_test(int cpu, struct device *dev);
 extern struct attribute *plat_ifs_attrs[];
 extern struct attribute *plat_ifs_array_attrs[];
 
+static inline void ifs_fpu_begin(void)
+{
+	/*
+	 * The AMX state must be initialized prior to executing In-Field
+	 * Scan tests, according to Intel SDM.
+	 */
+	kernel_fpu_begin_mask(KFPU_AMX);
+}
+
+static inline void ifs_fpu_end(void)
+{
+	kernel_fpu_end();
+}
+
 #endif
diff --git a/drivers/platform/x86/intel/ifs/runtest.c b/drivers/platform/x86/intel/ifs/runtest.c
index 95b4b71fab53..a35eac7c0b44 100644
--- a/drivers/platform/x86/intel/ifs/runtest.c
+++ b/drivers/platform/x86/intel/ifs/runtest.c
@@ -188,6 +188,9 @@ static int doscan(void *data)
 	/* Only the first logical CPU on a core reports result */
 	first = cpumask_first(cpu_smt_mask(cpu));
 
+	/* Prepare FPU state before entering the rendezvous loop*/
+	ifs_fpu_begin();
+
 	wait_for_sibling_cpu(&scan_cpus_in, NSEC_PER_SEC);
 
 	/*
@@ -199,6 +202,9 @@ static int doscan(void *data)
 	 * are processed in a single pass) before it retires.
 	 */
 	wrmsrl(MSR_ACTIVATE_SCAN, params->activate->data);
+
+	ifs_fpu_end();
+
 	rdmsrl(MSR_SCAN_STATUS, status.data);
 
 	trace_ifs_status(ifsd->cur_batch, start, stop, status.data);
-- 
2.34.1