On Tue, Jul 09, 2024 at 10:34:42PM -0700, Andrew Morton wrote: > > The patch titled > Subject: mm: fix PTE_AF handling in fault path on architectures with HW AF support > has been added to the -mm mm-hotfixes-unstable branch. Its filename is > mm-fix-pte_af-handling-in-fault-path-on-architectures-with-hw-af-support.patch This looks like v1 not v2? > This patch will shortly appear at > https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-pte_af-handling-in-fault-path-on-architectures-with-hw-af-support.patch > > This patch will later appear in the mm-hotfixes-unstable branch at > git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm > > Before you just go and hit "reply", please: > a) Consider who else should be cc'ed > b) Prefer to cc a suitable mailing list as well > c) Ideally: find the original patch on the mailing list and do a > reply-to-all to that, adding suitable additional cc's > > *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** > > The -mm tree is included into linux-next via the mm-everything > branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm > and is updated there every 2-3 working days > > ------------------------------------------------------ > From: Ram Tummala <rtummala@xxxxxxxxxx> > Subject: mm: fix PTE_AF handling in fault path on architectures with HW AF support > Date: Tue, 9 Jul 2024 17:09:42 -0700 > > 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 (Access Flag) 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. > > Link: https://lkml.kernel.org/r/20240710000942.623704-1-rtummala@xxxxxxxxxx > Fixes: 3bd786f76de2 ("mm: convert do_set_pte() to set_pte_range()") > Signed-off-by: Ram Tummala <rtummala@xxxxxxxxxx> > Reviewed-by: Yin Fengwei <fengwei.yin@xxxxxxxxx> > Acked-by: David Hildenbrand <david@xxxxxxxxxx> > Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> > Cc: Alistair Popple <apopple@xxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > --- > > mm/memory.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > --- a/mm/memory.c~mm-fix-pte_af-handling-in-fault-path-on-architectures-with-hw-af-support > +++ a/mm/memory.c > @@ -4681,7 +4681,7 @@ void set_pte_range(struct vm_fault *vmf, > { > struct vm_area_struct *vma = vmf->vma; > bool write = vmf->flags & FAULT_FLAG_WRITE; > - bool prefault = in_range(vmf->address, addr, nr * PAGE_SIZE); > + bool prefault = !in_range(vmf->address, addr, nr * PAGE_SIZE); > pte_t entry; > > flush_icache_pages(vma, page, nr); > _ > > Patches currently in -mm which might be from rtummala@xxxxxxxxxx are > > mm-fix-pte_af-handling-in-fault-path-on-architectures-with-hw-af-support.patch >
