mm: Expose untagging mask in /proc/$PID/status

Add a line in /proc/$PID/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 <[e-mail]>
Signed-off-by: Dave Hansen <[e-mail]>
Acked-by: Catalin Marinas <[e-mail]>
Acked-by: Peter Zijlstra (Intel) <[e-mail]>
Tested-by: Alexander Potapenko <[e-mail]>
Link: https://lore.kernel.org/all/20230312112612.31869-10-kirill.shutemov%40linux.intel.com

arch/arm64/include/asm/mmu_context.h

···
 unsigned long arm64_mm_context_get(struct mm_struct *mm);
 void arm64_mm_context_put(struct mm_struct *mm);
 
+#define mm_untag_mask mm_untag_mask
+static inline unsigned long mm_untag_mask(struct mm_struct *mm)
+{
+	return -1UL >> 8;
+}
+
 #include <asm-generic/mmu_context.h>
 
 #endif /* !__ASSEMBLY__ */

arch/sparc/include/asm/mmu_context_64.h

···
 	}
 }
 
+#define mm_untag_mask mm_untag_mask
+static inline unsigned long mm_untag_mask(struct mm_struct *mm)
+{
+       return -1UL >> adi_nbits();
+}
+
 #include <asm-generic/mmu_context.h>
 
 #endif /* !(__ASSEMBLY__) */

arch/x86/include/asm/mmu_context.h

···
 	mm->context.untag_mask = oldmm->context.untag_mask;
 }
 
+#define mm_untag_mask mm_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;

fs/proc/array.c

···
 #include <linux/user_namespace.h>
 #include <linux/fs_struct.h>
 #include <linux/kthread.h>
+#include <linux/mmu_context.h>
 
 #include <asm/processor.h>
 #include "internal.h"
···
 	seq_printf(m, "THP_enabled:\t%d\n", thp_enabled);
 }
 
+static inline void task_untag_mask(struct seq_file *m, struct mm_struct *mm)
+{
+	seq_printf(m, "untag_mask:\t%#lx\n", mm_untag_mask(mm));
+}
+
 int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
 			struct pid *pid, struct task_struct *task)
 {
···
 		task_mem(m, mm);
 		task_core_dumping(m, task);
 		task_thp_status(m, mm);
+		task_untag_mask(m, mm);
 		mmput(mm);
 	}
 	task_sig(m, task);

include/linux/mmu_context.h

···
 # define task_cpu_possible(cpu, p)	cpumask_test_cpu((cpu), task_cpu_possible_mask(p))
 #endif
 
+#ifndef mm_untag_mask
+static inline unsigned long mm_untag_mask(struct mm_struct *mm)
+{
+	return -1UL;
+}
+#endif
+
 #endif