Re: [PATCH 3/3] x86: mm: add x86_64 support for page table check

[Jiri Slaby]

On 02. 12. 21, 10:59, Jiri Slaby wrote:
> On 01. 12. 21, 14:55, Pasha Tatashin wrote:
> > On Wed, Dec 1, 2021 at 3:44 AM Jiri Slaby <jirislaby@xxxxxxxxxx> wrote:
> > > On 01. 12. 21, 9:00, Jiri Slaby wrote:
> > > > On 23. 11. 21, 22:48, Pasha Tatashin wrote:
> > > > > 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