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 patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------ From: Ram Tummala rtummala@nvidia.com 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@nvidia.com Fixes: 3bd786f76de2 ("mm: convert do_set_pte() to set_pte_range()") Signed-off-by: Ram Tummala rtummala@nvidia.com Reviewed-by: Yin Fengwei fengwei.yin@intel.com Acked-by: David Hildenbrand david@redhat.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Alistair Popple apopple@nvidia.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
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@nvidia.com are
mm-fix-pte_af-handling-in-fault-path-on-architectures-with-hw-af-support.patch