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

[Jinjie Ruan <ruanjinjie@huawei.com>]

On 7/14/2026 5:37 PM, Vladimir Murzin wrote:
> On 7/10/26 04:28, Jinjie Ruan wrote:
>>> @@ -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 mean that the return point of hibernate_exit() has already restored
the interrupt mask with local_daif_restore().

> 
> 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=--)

I encountered some problems when trying to enter the
swsusp_arch_resume() process on QEMU.

Considering that this is the key code, it is necessary to mask the debug
and serror exception , and also to mask ALLINT.

Therefore, LGTM except for the noreturn issue.

Reviewed-by: Jinjie Ruan <ruanjinjie@huawei.com>

>  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
>