[PATCH] kho: check fdt_phys in is_kho_boot()

[PATCH] kho: check fdt_phys in is_kho_boot()

[Greg Thelen]

During arm64 setup_arch(), efi_init() -> reserve_regions() calls
is_kho_boot() before arm64_memblock_init() initializes memstart_addr.
At this point memstart_addr still holds its initial sentinel value (-1).

When booting via kexec with KHO enabled, kho_populate() sets
kho_in.fdt_phys from the /chosen FDT node. Calling is_kho_boot() ->
kho_get_fdt() invokes phys_to_virt(kho_in.fdt_phys), which evaluates
PHYS_OFFSET and triggers VM_BUG_ON(memstart_addr & 1) on arm64 kernels
built with CONFIG_DEBUG_VM=y:

  kernel BUG at ./arch/arm64/include/asm/memory.h:377!
  Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
  Call trace:
   is_kho_boot+0x2c/0x38 (P)
   efi_init+0x94/0xf8
   setup_arch+0xf0/0x240
   start_kernel+0x84/0x490
   __primary_switched+0x88/0x98

Check kho_in.fdt_phys directly in is_kho_boot() instead of calling
kho_get_fdt() so that early boot callers do not invoke phys_to_virt()
before the linear map offset is initialized.

Fixes: d6d511639185 ("kexec: introduce is_kho_boot()")
Assisted-by: Gemini:gemini-3.8-flash
Signed-off-by: Greg Thelen <gthelen@google.com>
---
 kernel/liveupdate/kexec_handover.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 7c4d86daf86d..d81baa38497f 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -1630,7 +1630,7 @@ EXPORT_SYMBOL_GPL(kho_restore_free);
  */
 bool is_kho_boot(void)
 {
-	return !!kho_get_fdt();
+	return !!kho_in.fdt_phys;
 }
 EXPORT_SYMBOL_GPL(is_kho_boot);
 
-- 
2.56.0.257.gf7497c7d27-goog

Re: [PATCH] kho: check fdt_phys in is_kho_boot()

[Pratyush Yadav]

On Thu, Oct 22 2026, Greg Thelen wrote:

> During arm64 setup_arch(), efi_init() -> reserve_regions() calls
> is_kho_boot() before arm64_memblock_init() initializes memstart_addr.
> At this point memstart_addr still holds its initial sentinel value (-1).
>
> When booting via kexec with KHO enabled, kho_populate() sets
> kho_in.fdt_phys from the /chosen FDT node. Calling is_kho_boot() ->
> kho_get_fdt() invokes phys_to_virt(kho_in.fdt_phys), which evaluates
> PHYS_OFFSET and triggers VM_BUG_ON(memstart_addr & 1) on arm64 kernels
> built with CONFIG_DEBUG_VM=y:
>
>   kernel BUG at ./arch/arm64/include/asm/memory.h:377!
>   Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
>   Call trace:
>    is_kho_boot+0x2c/0x38 (P)
>    efi_init+0x94/0xf8
>    setup_arch+0xf0/0x240
>    start_kernel+0x84/0x490
>    __primary_switched+0x88/0x98
>
> Check kho_in.fdt_phys directly in is_kho_boot() instead of calling
> kho_get_fdt() so that early boot callers do not invoke phys_to_virt()
> before the linear map offset is initialized.
>
> Fixes: d6d511639185 ("kexec: introduce is_kho_boot()")
> Assisted-by: Gemini:gemini-3.8-flash
> Signed-off-by: Greg Thelen <gthelen@google.com>

Reviewed-by: Pratyush Yadav (Google) <pratyush@kernel.org>

[...]

-- 
Regards,
Pratyush Yadav

Re: [PATCH] kho: check fdt_phys in is_kho_boot()

[Mike Rapoport]

Hi,

On Thu, Oct 22, 2026 at 10:45:18PM -0700, Greg Thelen wrote:
> During arm64 setup_arch(), efi_init() -> reserve_regions() calls
> is_kho_boot() before arm64_memblock_init() initializes memstart_addr.
> At this point memstart_addr still holds its initial sentinel value (-1).
> 
> When booting via kexec with KHO enabled, kho_populate() sets
> kho_in.fdt_phys from the /chosen FDT node. Calling is_kho_boot() ->
> kho_get_fdt() invokes phys_to_virt(kho_in.fdt_phys), which evaluates
> PHYS_OFFSET and triggers VM_BUG_ON(memstart_addr & 1) on arm64 kernels
> built with CONFIG_DEBUG_VM=y:

Can't see the forest for the trees ;-)

Can you please translate the gist of the issue from LLMish to English?
 
>   kernel BUG at ./arch/arm64/include/asm/memory.h:377!
>   Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
>   Call trace:
>    is_kho_boot+0x2c/0x38 (P)
>    efi_init+0x94/0xf8
>    setup_arch+0xf0/0x240
>    start_kernel+0x84/0x490
>    __primary_switched+0x88/0x98
> 
> Check kho_in.fdt_phys directly in is_kho_boot() instead of calling
> kho_get_fdt() so that early boot callers do not invoke phys_to_virt()
> before the linear map offset is initialized.
> 
> Fixes: d6d511639185 ("kexec: introduce is_kho_boot()")
> Assisted-by: Gemini:gemini-3.8-flash
> Signed-off-by: Greg Thelen <gthelen@google.com>
> ---
>  kernel/liveupdate/kexec_handover.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> index 7c4d86daf86d..d81baa38497f 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -1630,7 +1630,7 @@ EXPORT_SYMBOL_GPL(kho_restore_free);
>   */
>  bool is_kho_boot(void)
>  {
> -	return !!kho_get_fdt();
> +	return !!kho_in.fdt_phys;
>  }
>  EXPORT_SYMBOL_GPL(is_kho_boot);
>  
> -- 
> 2.56.0.257.gf7497c7d27-goog
> 

-- 
Sincerely yours,
Mike.