[RFC PATCH 23/23] x86/process: Reset hardware history in context switch

[Ricardo Neri]

Reset the classification history of the current task when switching to
the next task. Hardware will start anew the classification of the next
running task.

Cc: Ben Segall <bsegall@xxxxxxxxxx>
Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Cc: Len Brown <len.brown@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Cc: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Tim C. Chen <tim.c.chen@xxxxxxxxx>
Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/hreset.h | 30 ++++++++++++++++++++++++++++++
 arch/x86/kernel/cpu/common.c  | 10 ++++++++++
 arch/x86/kernel/process_32.c  |  3 +++
 arch/x86/kernel/process_64.c  |  3 +++
 4 files changed, 46 insertions(+)
 create mode 100644 arch/x86/include/asm/hreset.h

diff --git a/arch/x86/include/asm/hreset.h b/arch/x86/include/asm/hreset.h
new file mode 100644
index 000000000000..d68ca2fb8642
--- /dev/null
+++ b/arch/x86/include/asm/hreset.h
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_HRESET_H
+
+/**
+ * HRESET - History reset. Available since binutils v2.36.
+ *
+ * Request the processor to reset the history of task classification on the
+ * current logical processor. The history components to be
+ * reset are specified in %eax. Only bits specified in CPUID(0x20).EBX
+ * and enabled in the IA32_HRESET_ENABLE MSR can be selected.
+ *
+ * The assembly code looks like:
+ *
+ *	hreset %eax
+ *
+ * The corresponding machine code looks like:
+ *
+ *	F3 0F 3A F0 ModRM Imm
+ *
+ * The value of ModRM is 0xc0 to specify %eax register addressing.
+ * The ignored immediate operand is set to 0.
+ *
+ * The instruction is documented in the Intel SDM.
+ */
+
+#define __ASM_HRESET  ".byte 0xf3, 0xf, 0x3a, 0xf0, 0xc0, 0x0"
+
+void reset_hardware_history(void);
+
+#endif /* _ASM_X86_HRESET_H */
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 108642fe6761..4622a0ebf8a1 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -52,6 +52,7 @@
 #include <asm/cpu.h>
 #include <asm/mce.h>
 #include <asm/msr.h>
+#include <asm/hreset.h>
 #include <asm/memtype.h>
 #include <asm/microcode.h>
 #include <asm/microcode_intel.h>
@@ -413,6 +414,15 @@ static __always_inline void setup_umip(struct cpuinfo_x86 *c)
 
 static u32 hardware_history_features __read_mostly;
 
+void reset_hardware_history(void)
+{
+	if (!static_cpu_has(X86_FEATURE_HRESET))
+		return;
+
+	asm volatile("mov %0, %%eax;" __ASM_HRESET "\n" : :
+		     "r" (hardware_history_features) : "%rax");
+}
+
 static __always_inline void setup_hreset(struct cpuinfo_x86 *c)
 {
 	if (!cpu_feature_enabled(X86_FEATURE_HRESET))
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 2f314b170c9f..74d8ad83e0b3 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -52,6 +52,7 @@
 #include <asm/switch_to.h>
 #include <asm/vm86.h>
 #include <asm/resctrl.h>
+#include <asm/hreset.h>
 #include <asm/proto.h>
 
 #include "process.h"
@@ -214,6 +215,8 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	/* Load the Intel cache allocation PQR MSR. */
 	resctrl_sched_in();
 
+	reset_hardware_history();
+
 	return prev_p;
 }
 
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 1962008fe743..0b175f30f359 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -53,6 +53,7 @@
 #include <asm/xen/hypervisor.h>
 #include <asm/vdso.h>
 #include <asm/resctrl.h>
+#include <asm/hreset.h>
 #include <asm/unistd.h>
 #include <asm/fsgsbase.h>
 #ifdef CONFIG_IA32_EMULATION
@@ -657,6 +658,8 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	/* Load the Intel cache allocation PQR MSR. */
 	resctrl_sched_in();
 
+	reset_hardware_history();
+
 	return prev_p;
 }
 
-- 
2.25.1