Re: [RFC PATCH 03/36] arm64: hibernate: mask DAIF before restoring hibernated kernel

On 7/10/26 04:28, Jinjie Ruan wrote:

quoted

@@ -465,9 +466,21 @@ int __nocfi swsusp_arch_resume(void)
 	if (el2_reset_needed())
 		__hyp_set_vectors(el2_vectors);
 
+	/*
+	 * It is necessary to mask all DAIF exceptions here as:
+	 *
+	 * - The copy of swsusp_arch_suspend_exit() in the hibernation
+	 *   text cannot handle taking any exceptions.
+	 *
+	 * - The suspended kernel masked all DAIF exceptions in
+	 *   swsusp_arch_resume(), and expects to be re-entered in the
+	 *   same state : with all DAIF exceptions masked.
+	 */
+	flags = local_daif_save();
 	hibernate_exit(virt_to_phys(tmp_pg_dir), resume_hdr.ttbr1_el1,
 		       resume_hdr.reenter_kernel, restore_pblist,
 		       resume_hdr.__hyp_stub_vectors, virt_to_phys(zero_page));
+	local_daif_restore(flags);

I believe that the local_daif_save() here is also unnecessary because
hibernate_exit() returns from the "return 0 branch" of
__cpu_suspend_enter() in swsusp_arch_suspend(), and before that,
local_daif_save() has already been called to mask all exceptions.

swsusp_arch_suspend(void)
    -> flags = local_daif_save();
    -> if (__cpu_suspend_enter(&state)) {
           ...
        } else {                // _cpu_resume <- hibernate_exit()

           ...
           in_suspend = 0;
           ...
        }
     -> local_daif_restore(flags);

I'm not sure I follow, we are protecting path

...
load_image_and_restore()
  -> hibernation_restore()
     -> resume_target_kernel()
        -> local_irq_disable()
        -> swsusp_arch_resume()
	  -> swsusp_arch_suspend_exit (aka hibernate_exit())
	     -> ...


issue can be easily observed with debug diff bellow applied on top of the
series

diff --git a/arch/arm64/kernel/hibernate.c b/arch/arm64/kernel/hibernate.c
index 4dd40593f736..709f5f4c420a 100644
--- a/arch/arm64/kernel/hibernate.c
+++ b/arch/arm64/kernel/hibernate.c

@@ -476,6 +476,7 @@ int __nocfi swsusp_arch_resume(void)
         *   swsusp_arch_resume(), and expects to be re-entered in the
         *   same state : with all DAIF exceptions masked.
         */
+       arm64_debug_exc_context(CRITICAL_CONTEXT);
        flags = local_all_irqs_save_mask(CRITICAL_CONTEXT);
        hibernate_exit(virt_to_phys(tmp_pg_dir), resume_hdr.ttbr1_el1,
                       resume_hdr.reenter_kernel, restore_pblist,

That would generate warning when run on qemu

 ------------[ cut here ]------------
 Unexpected DAIF+ALLINT: 0xc0 + 0x0 (expected 0x3c0 + 0x2000)
 WARNING: ./arch/arm64/include/asm/interrupts/common_flags.h:175 at swsusp_arch_resume+0x2d0/0x32c, CPU#0: sh/100
 Modules linked in:
 CPU: 0 UID: 0 PID: 100 Comm: sh Not tainted 7.2.0-rc2-00041-gc07d2a0843b2-dirty #288 PREEMPTLAZY 
 Hardware name: linux,dummy-virt (DT)
 pstate: 614000c5 (nZCv daIF -ALLINT +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
 pc : swsusp_arch_resume+0x2d0/0x32c
 lr : swsusp_arch_resume+0x2d0/0x32c
 sp : ffff800081adba80
 x29: ffff800081adbad0 x28: fff00000024ff000 x27: 0000000000000000
 x26: 0000000000000000 x25: 0000000000000000 x24: ffff8000815cd000
 x23: ffff8000815b4000 x22: ffff8000815c28d8 x21: ffff8000815c2000
 x20: fff000000a839000 x19: 0000000000000000 x18: 0000000000000006
 x17: 0000000000000000 x16: 0000000000000000 x15: ffff800081adb64f
 x14: ffff800081adb470 x13: ffff800101adb647 x12: 000000648200003c
 x11: ffff8000815cd8e8 x10: 0000000000000161 x9 : ffff8000815cd8e8
 x8 : 0000000000000162 x7 : ffff8000816258e8 x6 : ffff8000816258e8
 x5 : 3fffffffffffefff x4 : bffffffffffff000 x3 : 0000000000000000
 x2 : 0000000000000000 x1 : 0000000000000000 x0 : fff00000024ff000
 Call trace:
  swsusp_arch_resume+0x2d0/0x32c (P)
  hibernation_restore+0xe0/0x1a4
  load_image_and_restore+0x60/0xb0
  hibernate+0x228/0x374
  state_store+0xe8/0xf4
  kobj_attr_store+0x18/0x34
  sysfs_kf_write+0x5c/0x78
  kernfs_fop_write_iter+0x130/0x200
  vfs_write+0x20c/0x380
  ksys_write+0x70/0x110
  __arm64_sys_write+0x1c/0x28
  invoke_syscall.constprop.0+0x58/0x100
  do_el0_svc+0x40/0xc0
  el0_svc+0x200/0xa0c
  el0t_64_sync_handler+0x110/0x20c
  el0t_64_sync+0x1ac/0x1b0
 ---[ end trace 0000000000000000 ]---

Cheers
Vladimir