Re: [PATCH 1/2] x86: mm: ptdump: Calculate effective permissions correctly

From: Jan Beulich
Date: Wed May 27 2020 - 11:15:23 EST

On 21.05.2020 17:23, Steven Price wrote:
> By switching the x86 page table dump code to use the generic code the
> effective permissions are no longer calculated correctly because the
> note_page() function is only called for *leaf* entries. To calculate the
> actual effective permissions it is necessary to observe the full
> hierarchy of the page tree.
> Introduce a new callback for ptdump which is called for every entry and
> can therefore update the prot_levels array correctly. note_page() can
> then simply access the appropriate element in the array.
> Reported-by: Jan Beulich <jbeulich@xxxxxxxx>
> Fixes: 2ae27137b2db ("x86: mm: convert dump_pagetables to use walk_page_range")
> Signed-off-by: Steven Price <steven.price@xxxxxxx>

This (with the later correction) and the 2nd patch
Tested-by: Jan Beulich <jbeulich@xxxxxxxx>

It allowed me to go and finally find why under Xen there was still
a single W+X mapping left - another bug, another patch.

Thanks, Jan