On Wed, 20 Apr 2022 09:50:52 +0200 Max Krummenacher <max.oss.09@xxxxxxxxx> wrote: > > > > Unfortunately, the vmlinux.xz file I downloaded from the link below > > seems to be different from the one that produced the crash, given that > > the LR address of c04cfeb8 does not seem to correspond with > > handle_mm_fault+0x60c/0xed0. > > > > Can you please double check the artifacts? > > Commit "mm: check against orig_pte for finish_fault()" introduced this, > i.e. on yesterdays next reverting a066bab3c0eb made a i.MX6 boot again. > A fix is discussed here: > > https://lore.kernel.org/all/YliNP7ADcdc4Puvs@xz-m1.local/ > Thanks for finding that. I have Peter's fix queued and shall push out a snapshot later today, for integration into linux-next. From: Peter Xu <peterx@xxxxxxxxxx> Subject: mm-check-against-orig_pte-for-finish_fault-fix fix crash reported by Marek Link: https://lkml.kernel.org/r/Ylb9rXJyPm8/ao8f@xz-m1.local Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> Cc: Alistair Popple <apopple@xxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Jerome Glisse <jglisse@xxxxxxxxxx> Cc: "Kirill A . Shutemov" <kirill@xxxxxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> Cc: Nadav Amit <nadav.amit@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- --- a/include/linux/mm_types.h~mm-check-against-orig_pte-for-finish_fault-fix +++ a/include/linux/mm_types.h @@ -814,6 +814,8 @@ typedef struct { * @FAULT_FLAG_UNSHARE: The fault is an unsharing request to unshare (and mark * exclusive) a possibly shared anonymous page that is * mapped R/O. + * @FAULT_FLAG_ORIG_PTE_VALID: whether the fault has vmf->orig_pte cached. + * We should only access orig_pte if this flag set. * * About @FAULT_FLAG_ALLOW_RETRY and @FAULT_FLAG_TRIED: we can specify * whether we would allow page faults to retry by specifying these two @@ -850,6 +852,7 @@ enum fault_flag { FAULT_FLAG_INSTRUCTION = 1 << 8, FAULT_FLAG_INTERRUPTIBLE = 1 << 9, FAULT_FLAG_UNSHARE = 1 << 10, + FAULT_FLAG_ORIG_PTE_VALID = 1 << 11, }; #endif /* _LINUX_MM_TYPES_H */ --- a/mm/memory.c~mm-check-against-orig_pte-for-finish_fault-fix +++ a/mm/memory.c @@ -4194,6 +4194,15 @@ void do_set_pte(struct vm_fault *vmf, st set_pte_at(vma->vm_mm, addr, vmf->pte, entry); } +static bool vmf_pte_changed(struct vm_fault *vmf) +{ + if (vmf->flags & FAULT_FLAG_ORIG_PTE_VALID) { + return !pte_same(*vmf->pte, vmf->orig_pte); + } + + return !pte_none(*vmf->pte); +} + /** * finish_fault - finish page fault once we have prepared the page to fault * @@ -4252,7 +4261,7 @@ vm_fault_t finish_fault(struct vm_fault vmf->address, &vmf->ptl); ret = 0; /* Re-check under ptl */ - if (likely(pte_same(*vmf->pte, vmf->orig_pte))) + if (likely(!vmf_pte_changed(vmf))) do_set_pte(vmf, page, vmf->address); else ret = VM_FAULT_NOPAGE; @@ -4720,13 +4729,7 @@ static vm_fault_t handle_pte_fault(struc * concurrent faults and from rmap lookups. */ vmf->pte = NULL; - /* - * Always initialize orig_pte. This matches with below - * code to have orig_pte to be the none pte if pte==NULL. - * This makes the rest code to be always safe to reference - * it, e.g. in finish_fault() we'll detect pte changes. - */ - pte_clear(vmf->vma->vm_mm, vmf->address, &vmf->orig_pte); + vmf->flags &= ~FAULT_FLAG_ORIG_PTE_VALID; } else { /* * If a huge pmd materialized under us just retry later. Use @@ -4750,6 +4753,7 @@ static vm_fault_t handle_pte_fault(struc */ vmf->pte = pte_offset_map(vmf->pmd, vmf->address); vmf->orig_pte = *vmf->pte; + vmf->flags |= FAULT_FLAG_ORIG_PTE_VALID; /* * some architectures can have larger ptes than wordsize, _
