Re: [PATCH] arm64: hibernate: pass HVC_SET_VECTORS args to the resume hvc

[Will Deacon <will@kernel.org>]

[+Maz, Pasha and James]

On Sun, Aug 09, 2026 at 09:36:15PM +0000, Bradley Morgan wrote:
> swsusp_arch_suspend_exit() reinstalls the restored kernel's hyp stub
> vectors with an hvc, but never passes the arguments. x0 is not set to
> HVC_SET_VECTORS and x1 is not set to the vector address, so the stub
> dispatch falls through and returns without writing vbar_el2. EL2 is
> left pointing at the trans_pgd copy of the vectors, a page that
> swsusp_free() releases right after resume.
> 
> Set the arguments up the same way __hyp_set_vectors() does.
> 
> Fixes: 788bfdd97434 ("arm64: trans_pgd: hibernate: Add trans_pgd_copy_el2_vectors")
> Cc: stable@vger.kernel.org
> Signed-off-by: Bradley Morgan <include@grrlz.net>
> ---
>  arch/arm64/kernel/hibernate-asm.S | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm64/kernel/hibernate-asm.S b/arch/arm64/kernel/hibernate-asm.S
> index 0e1d9c3c6a93..2baefe7a82d3 100644
> --- a/arch/arm64/kernel/hibernate-asm.S
> +++ b/arch/arm64/kernel/hibernate-asm.S
> @@ -89,6 +89,8 @@ alternative_insn "dc cvau, x4",  "dc civac, x4",  ARM64_WORKAROUND_CLEAN_CACHE
>  	isb
>  
>  	cbz	x24, 3f		/* Do we need to re-initialise EL2? */
> +	mov	x1, x24
> +	mov	x0, #HVC_SET_VECTORS
>  	hvc	#0
>  3:	ret
>  SYM_CODE_END(swsusp_arch_suspend_exit)

I'm having a really hard time figuring out what's supposed to be going
on here!

The original hibernation code added by James in 82869ac57b5d ("arm64:
kernel: Add support for hibernate/suspend-to-disk") unconditionally
set the vectors in the exception handler:

+el1_sync:
+       msr     vbar_el2, x24
+       eret
+ENDPROC(el1_sync)

However, it _also_ set the vectors from C code in swsusp_arch_resume():

+       if (el2_reset_needed()) {
+               phys_addr_t el2_vectors = phys_hibernate_exit;  /* base */
+               el2_vectors += hibernate_el2_vectors -
+                              __hibernate_exit_text_start;     /* offset */
+
+               __hyp_set_vectors(el2_vectors);
+       }

Later, Pasha refactored the assembly so that it could be shared with
kexec in 788bfdd97434 ("arm64: trans_pgd: hibernate: Add
trans_pgd_copy_el2_vectors"), however this added arguments to the
exception handler without updating the hypercall on the hibernation path.

So I think we need to figure out:

0. Whether this code is actually broken atm (I have a feeling it might
   happen to work)
1. Why the original hibernation code set the vectors twice.
2. Assuming they only need to be set once, whether we can drop the hvc
   from the swsusp_arch_suspend_exit assembly code entirely.
3. Whether we can then drop the HVC_SET_VECTORS handling from this set
   of vectors.

Will