linux-kernel - [PATCH v3 3/3] platform/x86/intel/ifs: Initialize FPU states for the scan test

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Date: Thu, 30 May 2024 12:27:39 -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,
	sathyanarayanan.kuppuswamy@...ux.intel.com,
	chang.seok.bae@...el.com
Subject: [PATCH v3 3/3] platform/x86/intel/ifs: Initialize FPU states for the scan test

The In-Field Scan process aborts if AMX state is not in initialized
state. Use fpu_reset_fpregs() to ensure AMX state is initialized before
entering the rendezvous loop.

Suggested-by: Dave Hansen <dave.hansen@...ux.intel.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Tested-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
---
V2 -> V3: Use fpu_reset_user_fpregs().
	  Thanks to everyone who provided tags on previous versions. Due
	  to the code change, I felt it necessary to revoke them, but the
	  high-level logic remains the same.

V1 -> V2: Revised the changelog (Ashok), added a space to the code comment
	  (Ilpo), and included the header file explicitly (0-day).
---
 drivers/platform/x86/intel/ifs/ifs.h     | 1 +
 drivers/platform/x86/intel/ifs/runtest.c | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/drivers/platform/x86/intel/ifs/ifs.h b/drivers/platform/x86/intel/ifs/ifs.h
index 56b9f3e3cf76..5e7ba94b4054 100644
--- a/drivers/platform/x86/intel/ifs/ifs.h
+++ b/drivers/platform/x86/intel/ifs/ifs.h
@@ -129,6 +129,7 @@
  */
 #include <linux/device.h>
 #include <linux/miscdevice.h>
+#include <asm/fpu/api.h>
 
 #define MSR_ARRAY_BIST				0x00000105
 #define MSR_COPY_SCAN_HASHES			0x000002c2
diff --git a/drivers/platform/x86/intel/ifs/runtest.c b/drivers/platform/x86/intel/ifs/runtest.c
index 282e4bfe30da..68e128ea57ed 100644
--- a/drivers/platform/x86/intel/ifs/runtest.c
+++ b/drivers/platform/x86/intel/ifs/runtest.c
@@ -191,6 +191,10 @@ 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 */
+	kernel_fpu_begin();
+	fpu_reset_fpregs();
+
 	wait_for_sibling_cpu(&scan_cpus_in, NSEC_PER_SEC);
 
 	/*
@@ -202,6 +206,9 @@ static int doscan(void *data)
 	 * are processed in a single pass) before it retires.
 	 */
 	wrmsrl(MSR_ACTIVATE_SCAN, params->activate->data);
+
+	kernel_fpu_end();
+
 	rdmsrl(MSR_SCAN_STATUS, status.data);
 
 	trace_ifs_status(ifsd->cur_batch, start, stop, status.data);
-- 
2.34.1