Re: [tip: x86/urgent] x86/mm/pat: Fix effective RW computation in lookup_address_in_pgd_attr()

[Nathan Chancellor <nathan@kernel.org>]

On Sun, Sep 06, 2026 at 07:50:26AM -0700, Dave Hansen wrote:
> On 9/4/26 21:42, Nathan Chancellor wrote:
> > I just bisected the following warning on a couple of my test machines to
> > commit 453e78594434 ("x86/mm/pat: Fix effective RW computation in
> > lookup_address_in_pgd_attr()") in next-20260904.
> ...
> > If there is any information I can provide to help debug this, I am happy
> > to provide it.
> 
> Well, the thing you bisected to is the patch that fixes the warning. The

Hmmm, I don't see a warning prior to this patch though. Do you mean that
this patch is just revealing the bad behavior that you mention below?

> actual issue comes from:
> 
>         if (pages == &its_pages)
>                 set_memory_x((unsigned long)page, 1);
> 
> which its_alloc() does on an execmem allocation. Any chance you could
> get the output of:
> 
> 	/sys/kernel/debug/page_tables/current_kernel
> 
> for the page that page that it's complaining about? I'm curious if this
> is temporary or permanent.

Sure. For

   CPA detected W^X violation: 8000000000000123 -> 0000000000000123 range: 0xffffffffc0200000 - 0xffffffffc0200fff PFN 100e00

I think it is this line if I understand correctly?

  0xffffffffc0200000-0xffffffffc0400000           2M     ro         PSE     GLB x  pmd

-- 
Cheers,
Nathan