linux/modules/pagetables: fix building on Linux 6.15

Linux 6.15 removed `struct pcpu_hot` and used `current_task` again.
https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a1e4cc0155ad577adc3a2c563fc5eec625945ce7

Building on Fedora 43 reported:

    make -C /lib/modules/6.15.0-0.rc0.20250327git1a9239bb4253.5.fc43.x86_64/build M=/shared/linux/modules modules
      CC [M]  pagetables.o
    pagetables.c: In function ‘print_additional_desc’:
    pagetables.c:334:44: error: ‘pcpu_hot’ undeclared (first use in this function)
      334 |         describe_with_pointer(per_cpu_ptr(&pcpu_hot, 0), "percpu area");
          |                                            ^~~~~~~~
    pagetables.c:306:54: note: in definition of macro ‘describe_with_pointer’
      306 |                 unsigned long _ptr = (unsigned long)(ptr); \
          |                                                      ^~~
    /usr/src/kernels/6.15.0-0.rc0.20250327git1a9239bb4253.5.fc43.x86_64/include/linux/percpu-defs.h:238:9: note: in expansion of macro ‘__verify_pcpu_ptr’
      238 |         __verify_pcpu_ptr(ptr);                                         \
          |         ^~~~~~~~~~~~~~~~~
    pagetables.c:334:31: note: in expansion of macro ‘per_cpu_ptr’
      334 |         describe_with_pointer(per_cpu_ptr(&pcpu_hot, 0), "percpu area");
          |                               ^~~~~~~~~~~
    pagetables.c:334:44: note: each undeclared identifier is reported only once for each function it appears in
      334 |         describe_with_pointer(per_cpu_ptr(&pcpu_hot, 0), "percpu area");
          |                                            ^~~~~~~~
    pagetables.c:306:54: note: in definition of macro ‘describe_with_pointer’
      306 |                 unsigned long _ptr = (unsigned long)(ptr); \
          |                                                      ^~~
    /usr/src/kernels/6.15.0-0.rc0.20250327git1a9239bb4253.5.fc43.x86_64/include/linux/percpu-defs.h:238:9: note: in expansion of macro ‘__verify_pcpu_ptr’
      238 |         __verify_pcpu_ptr(ptr);                                         \
          |         ^~~~~~~~~~~~~~~~~
    pagetables.c:334:31: note: in expansion of macro ‘per_cpu_ptr’
      334 |         describe_with_pointer(per_cpu_ptr(&pcpu_hot, 0), "percpu area");
          |                               ^~~~~~~~~~~

Author: fishilico

linux/modules/pagetables.c

@@ -326,7 +326,13 @@ static void print_additional_desc(struct pg_state *st, unsigned long last_addr)
 	describe_with_pointer(&addr, "current stack");
 
 #ifdef CONFIG_X86
-# if LINUX_VERSION_CODE >= KERNEL_VERSION(6, 2, 0)
+# if LINUX_VERSION_CODE >= KERNEL_VERSION(6, 15, 0)
+	/* Commit a1e4cc0155ad ("x86/percpu: Move current_task to percpu hot
+	 * section") replaced pcpu_hot.current_task with current_task again.
+	 * Show where the percpu area is on x86, using current_task
+	 */
+	describe_with_pointer(per_cpu_ptr(&current_task, 0), "percpu area");
+# elif LINUX_VERSION_CODE >= KERNEL_VERSION(6, 2, 0)
 	/* Commit e57ef2ed97c1 ("x86: Put hot per CPU variables into a struct")
 	 * replaced current_task with pcpu_hot.current_task.
 	 * Show where the percpu area is on x86, using pcpu_hot