[PATCHv10 09/15] x86: Expose untagging mask in /proc/$PID/arch_status

[Kirill A. Shutemov]

Add a line in /proc/$PID/arch_status to report untag_mask. It can be
used to find out LAM status of the process from the outside. It is
useful for debuggers.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Tested-by: Alexander Potapenko <glider@xxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 arch/x86/include/asm/mmu_context.h | 10 +++++
 arch/x86/kernel/Makefile           |  2 +
 arch/x86/kernel/fpu/xstate.c       | 47 -----------------------
 arch/x86/kernel/proc.c             | 60 ++++++++++++++++++++++++++++++
 4 files changed, 72 insertions(+), 47 deletions(-)
 create mode 100644 arch/x86/kernel/proc.c

diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 5bd3d46685dc..b0e9ea23758b 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -103,6 +103,11 @@ static inline void dup_lam(struct mm_struct *oldmm, struct mm_struct *mm)
 	mm->context.untag_mask = oldmm->context.untag_mask;
 }
 
+static inline unsigned long mm_untag_mask(struct mm_struct *mm)
+{
+	return mm->context.untag_mask;
+}
+
 static inline void mm_reset_untag_mask(struct mm_struct *mm)
 {
 	mm->context.untag_mask = -1UL;
@@ -119,6 +124,11 @@ static inline void dup_lam(struct mm_struct *oldmm, struct mm_struct *mm)
 {
 }
 
+static inline unsigned long mm_untag_mask(struct mm_struct *mm)
+{
+	return -1UL;
+}
+
 static inline void mm_reset_untag_mask(struct mm_struct *mm)
 {
 }
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index f901658d9f7c..d99fd065aba8 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -143,6 +143,8 @@ obj-$(CONFIG_AMD_MEM_ENCRYPT)		+= sev.o
 
 obj-$(CONFIG_CFI_CLANG)			+= cfi.o
 
+obj-$(CONFIG_PROC_FS)			+= proc.o
+
 ###
 # 64 bit specific files
 ifeq ($(CONFIG_X86_64),y)
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index c8340156bfd2..838a6f0627fd 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -10,8 +10,6 @@
 #include <linux/mman.h>
 #include <linux/nospec.h>
 #include <linux/pkeys.h>
-#include <linux/seq_file.h>
-#include <linux/proc_fs.h>
 #include <linux/vmalloc.h>
 
 #include <asm/fpu/api.h>
@@ -1745,48 +1743,3 @@ long fpu_xstate_prctl(int option, unsigned long arg2)
 		return -EINVAL;
 	}
 }
-
-#ifdef CONFIG_PROC_PID_ARCH_STATUS
-/*
- * Report the amount of time elapsed in millisecond since last AVX512
- * use in the task.
- */
-static void avx512_status(struct seq_file *m, struct task_struct *task)
-{
-	unsigned long timestamp = READ_ONCE(task->thread.fpu.avx512_timestamp);
-	long delta;
-
-	if (!timestamp) {
-		/*
-		 * Report -1 if no AVX512 usage
-		 */
-		delta = -1;
-	} else {
-		delta = (long)(jiffies - timestamp);
-		/*
-		 * Cap to LONG_MAX if time difference > LONG_MAX
-		 */
-		if (delta < 0)
-			delta = LONG_MAX;
-		delta = jiffies_to_msecs(delta);
-	}
-
-	seq_put_decimal_ll(m, "AVX512_elapsed_ms:\t", delta);
-	seq_putc(m, '\n');
-}
-
-/*
- * Report architecture specific information
- */
-int proc_pid_arch_status(struct seq_file *m, struct pid_namespace *ns,
-			struct pid *pid, struct task_struct *task)
-{
-	/*
-	 * Report AVX512 state if the processor and build option supported.
-	 */
-	if (cpu_feature_enabled(X86_FEATURE_AVX512F))
-		avx512_status(m, task);
-
-	return 0;
-}
-#endif /* CONFIG_PROC_PID_ARCH_STATUS */
diff --git a/arch/x86/kernel/proc.c b/arch/x86/kernel/proc.c
new file mode 100644
index 000000000000..9765b4d05ce4
--- /dev/null
+++ b/arch/x86/kernel/proc.c
@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/proc_fs.h>
+#include <linux/sched/mm.h>
+#include <linux/seq_file.h>
+#include <uapi/asm/prctl.h>
+#include <asm/mmu_context.h>
+
+/*
+ * Report the amount of time elapsed in millisecond since last AVX512
+ * use in the task.
+ */
+static void avx512_status(struct seq_file *m, struct task_struct *task)
+{
+	unsigned long timestamp = READ_ONCE(task->thread.fpu.avx512_timestamp);
+	long delta;
+
+	if (!timestamp) {
+		/*
+		 * Report -1 if no AVX512 usage
+		 */
+		delta = -1;
+	} else {
+		delta = (long)(jiffies - timestamp);
+		/*
+		 * Cap to LONG_MAX if time difference > LONG_MAX
+		 */
+		if (delta < 0)
+			delta = LONG_MAX;
+		delta = jiffies_to_msecs(delta);
+	}
+
+	seq_put_decimal_ll(m, "AVX512_elapsed_ms:\t", delta);
+	seq_putc(m, '\n');
+}
+
+/*
+ * Report architecture specific information
+ */
+int proc_pid_arch_status(struct seq_file *m, struct pid_namespace *ns,
+			struct pid *pid, struct task_struct *task)
+{
+	struct mm_struct *mm;
+	unsigned long untag_mask = -1UL;
+
+	/*
+	 * Report AVX512 state if the processor and build option supported.
+	 */
+	if (cpu_feature_enabled(X86_FEATURE_AVX512F))
+		avx512_status(m, task);
+
+	mm = get_task_mm(task);
+	if (mm) {
+		untag_mask = mm_untag_mask(task->mm);
+		mmput(mm);
+	}
+
+	seq_printf(m, "untag_mask:\t%#lx\n", untag_mask);
+
+	return 0;
+}
-- 
2.38.0