On 10.07.24 02:09, Ram Tummala wrote:
Commit 3bd786f76de2 ("mm: convert do_set_pte() to set_pte_range()")
replaced do_set_pte() with set_pte_range() and that introduced a regression
in the following faulting path of non-anonymous vmas on CPUs with HW AF
support.
handle_pte_fault()
do_pte_missing()
do_fault()
do_read_fault() || do_cow_fault() || do_shared_fault()
finish_fault()
set_pte_range()
The polarity of prefault calculation is incorrect. This leads to prefault
being incorrectly set for the faulting address. The following if check will
incorrectly clear the PTE_AF bit instead of setting it and the access will
fault again on the same address due to the missing PTE_AF bit.
if (prefault && arch_wants_old_prefaulted_pte())
entry = pte_mkold(entry);
On a subsequent fault on the same address, the faulting path will see a non
NULL vmf->pte and instead of reaching the do_pte_missing() path, PTE_AF
will be correctly set in handle_pte_fault() itself.
Due to this bug, performance degradation in the fault handling path will be
observed due to unnecessary double faulting.
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 3bd786f76de2 ("mm: convert do_set_pte() to set_pte_range()")
Signed-off-by: Ram Tummala <rtummala@xxxxxxxxxx>
---
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
--
Cheers,
David / dhildenb
