Re: [PATCH 2/3] fs/proc/task_mmu: don't read young/dirty from a non-present PMD in smaps

[David Hildenbrand (Arm)]

On 11/11/26 12:38, Usama Arif wrote:
> smaps_pmd_entry() passes pmd_young(*pmd) and pmd_dirty(*pmd) to
> smaps_account() for every PMD, including migration and device-private
> entries, where those bits hold part of the swap offset rather than
> accessed/dirty state. smaps_pte_entry() only reads them when the entry
> is present.
> 
> On x86_64 the offset is stored inverted across bits 9-58, which overlap
> _PAGE_SAVED_DIRTY, so pmd_dirty() returns garbage: a clean 2MB
> device-private mapping is accounted as 2048 kB dirty, and lazyfree
> accounting is suppressed. pgtable_64.h also warns that the hardware can
> set the accessed and dirty bits on non-present entries by mistake.
> 
> Only read the bits when the PMD is present.
> 
> Fixes: c94b6923fa0a ("/proc/PID/smaps: Add PMD migration entry parsing")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Usama Arif <usama.arif@xxxxxxxxx>
> ---

Yes, thanks!

Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

-- 
Cheers,

David