On 02. 12. 21, 10:59, Jiri Slaby wrote:

On 01. 12. 21, 14:55, Pasha Tatashin wrote:

quoted

On Wed, Dec 1, 2021 at 3:44 AM Jiri Slaby [off-list ref] wrote:

quoted

On 01. 12. 21, 9:00, Jiri Slaby wrote:

quoted

On 23. 11. 21, 22:48, Pasha Tatashin wrote:

quoted

Add page table check hooks into routines that modify user page tables.

Hi,

I bisected to this as this causes crashes during modules load:

And it's not enough to unset CONFIG_PAGE_TABLE_CHECK_ENFORCED. I had to
unset CONFIG_PAGE_TABLE_CHECK completely to get rid of this.

Hi,

Thanks for reporting this. Seems like module load for some reasons
does not like the static branches. However, I was not able to repro
this. Could you please share your config and the module that you were
loading?

It's the openSUSE's -next config:
https://raw.githubusercontent.com/openSUSE/kernel-source/linux-next/config/x86_64/vanilla 


But with CONFIG_IWLMEI=n (as that fails to link).

One has to load i915, other modules (71 on my system) are apparently fine.

i915 tries to patch your `page_table_check_disabled' which is defined as 
`DEFINE_STATIC_KEY_TRUE_RO':
 > jump_label_add_module: key=__tracepoint_mmap_lock_released 
(ffffffff93f36d88) mod=0000000000000000
 > jump_label_add_module: key=hugetlb_free_vmemmap_enabled_key 
(ffffffff94873560) mod=0000000000000000
 > jump_label_add_module: key=devmap_managed_key (ffffffff94902700) 
mod=0000000000000000
 > jump_label_add_module: key=page_table_check_disabled 
(ffffffff939da760) mod=0000000000000000
 > BUG: unable to handle page fault for address: ffffffff939da768

Provided you EXPORT page_table_check_disabled and it can be used from 
modules, it can be barely marked as RO. So the below indeed fixes the 
problem for me:

--- a/mm/page_table_check.c
+++ b/mm/page_table_check.c

@@ -18,7 +18,7 @@ struct page_table_check {
  static bool __page_table_check_enabled __initdata =
 

IS_ENABLED(CONFIG_PAGE_TABLE_CHECK_ENFORCED);

-DEFINE_STATIC_KEY_TRUE_RO(page_table_check_disabled);
+DEFINE_STATIC_KEY_TRUE(page_table_check_disabled);
  EXPORT_SYMBOL(page_table_check_disabled);

  static int __init early_page_table_check_param(char *buf)

regards,

-- 
js
suse labs