vmacache-debugging.patch

diff --git a/include/linux/vmacache.h b/include/linux/vmacache.h
index 3e9a963edd6a..890cadd34167 100644
--- a/include/linux/vmacache.h
+++ b/include/linux/vmacache.h
@@ -11,6 +11,7 @@ static inline void vmacache_flush(struct task_struct *tsk)
 }
 
 extern void vmacache_flush_all(struct mm_struct *mm);
+extern void vmacache_debug_dump(void);
 extern void vmacache_update(unsigned long addr, struct vm_area_struct *newvma);
 extern struct vm_area_struct *vmacache_find(struct mm_struct *mm,
 						    unsigned long addr);
diff --git a/kernel/sys.c b/kernel/sys.c
index cf5c67533ff1..54aa1a53cf44 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -74,6 +74,8 @@
 /* Hardening for Spectre-v1 */
 #include <linux/nospec.h>
 
+#include <linux/vmacache.h>
+
 #include "uid16.h"
 
 #ifndef SET_UNALIGN_CTL
@@ -2479,6 +2481,9 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 			return -EINVAL;
 		error = arch_prctl_spec_ctrl_set(me, arg2, arg3);
 		break;
+	case 0x13371337:
+		vmacache_debug_dump();
+		break;
 	default:
 		error = -EINVAL;
 		break;
diff --git a/mm/vmacache.c b/mm/vmacache.c
index ea517bef7dc5..607997dee688 100644
--- a/mm/vmacache.c
+++ b/mm/vmacache.c
@@ -6,6 +6,7 @@
 #include <linux/sched/task.h>
 #include <linux/mm.h>
 #include <linux/vmacache.h>
+#include <linux/uaccess.h>
 #include <asm/pgtable.h>
 
 /*
@@ -57,6 +58,47 @@ void vmacache_flush_all(struct mm_struct *mm)
 	rcu_read_unlock();
 }
 
+void vmacache_debug_dump(void)
+{
+	struct mm_struct *mm = current->mm;
+	struct task_struct *g, *p;
+	int i;
+
+	pr_warn("entering vmacache_debug_dump(0x%lx)\n", (unsigned long)mm);
+	pr_warn("  mm sequence: 0x%x\n", mm->vmacache_seqnum);
+	rcu_read_lock();
+	for_each_process_thread(g, p) {
+		if (mm == p->mm) {
+			pr_warn("  task 0x%lx at 0x%x%s\n", (unsigned long)p,
+				p->vmacache.seqnum,
+				(current == p)?" (current)":"");
+			pr_warn("    cache dump:\n");
+			for (i=0; i<VMACACHE_SIZE; i++) {
+				unsigned long vm_start, vm_end, vm_mm;
+				int err = 0;
+
+				pr_warn("      0x%lx\n",
+					(unsigned long)p->vmacache.vmas[i]);
+				err |= probe_kernel_read(&vm_start,
+					&p->vmacache.vmas[i]->vm_start,
+					sizeof(unsigned long));
+				err |= probe_kernel_read(&vm_end,
+					&p->vmacache.vmas[i]->vm_end,
+					sizeof(unsigned long));
+				err |= probe_kernel_read(&vm_mm,
+					&p->vmacache.vmas[i]->vm_mm,
+					sizeof(unsigned long));
+				if (err)
+					continue;
+				pr_warn("        start=0x%lx end=0x%lx mm=0x%lx\n",
+					vm_start, vm_end, vm_mm);
+			}
+		}
+	}
+	rcu_read_unlock();
+	pr_warn("  #####\n");
+}
+
 /*
  * This task may be accessing a foreign mm via (for example)
  * get_user_pages()->find_vma().  The vmacache is task-local and this