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@vger.kernel.org Fixes: 3bd786f76de2 ("mm: convert do_set_pte() to set_pte_range()") Signed-off-by: Ram Tummala rtummala@nvidia.com
Acked-by: David Hildenbrand david@redhat.com