Messages in this thread |  | | Date | Tue, 8 Apr 2025 13:24:57 +0100 | | From | Lorenzo Stoakes <> | | Subject | Re: [PATCH v2] x86/mm/pat: (un)track_pfn_copy() fix + doc improvements |
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On Tue, Apr 08, 2025 at 10:59:50AM +0200, David Hildenbrand wrote: > We got a late smatch warning and some additional review feedback. > > smatch warnings: > mm/memory.c:1428 copy_page_range() error: uninitialized symbol 'pfn'. > > We actually use the pfn only when it is properly initialized; however, > we may pass an uninitialized value to a function -- although it will not > use it that likely still is UB in C. > > So let's just fix it by always initializing pfn in the caller of > track_pfn_copy(), and improving the documentation of track_pfn_copy(). > > While at it, clarify the doc of untrack_pfn_copy(), that internal checks > make sure if we actually have to untrack anything. > > Fixes: dc84bc2aba85 ("x86/mm/pat: Fix VM_PAT handling when fork() fails in copy_page_range()") > Reported-by: kernel test robot <lkp@intel.com> > Reported-by: Dan Carpenter <error27@gmail.com> > Closes: https://lore.kernel.org/r/202503270941.IFILyNCX-lkp@intel.com/ > Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> > Cc: Dave Hansen <dave.hansen@linux.intel.com> > Cc: Andy Lutomirski <luto@kernel.org> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Borislav Petkov <bp@alien8.de> > Cc: Rik van Riel <riel@surriel.com> > Cc: "H. Peter Anvin" <hpa@zytor.com> > Cc: Linus Torvalds <torvalds@linux-foundation.org> > Signed-off-by: David Hildenbrand <david@redhat.com> > --- > > v1 -> v2: > * Adjust the doc instead of initializing the pfn whenever returning 0 > * Decided to keep Lorenzo's RB :)
All good with me :) the patch in this form is fine!
> * Retested > > --- > include/linux/pgtable.h | 9 ++++++--- > mm/memory.c | 2 +- > 2 files changed, 7 insertions(+), 4 deletions(-) > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index e2b705c149454..b50447ef1c921 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -1511,8 +1511,9 @@ static inline void track_pfn_insert(struct vm_area_struct *vma, pgprot_t *prot, > > /* > * track_pfn_copy is called when a VM_PFNMAP VMA is about to get the page > - * tables copied during copy_page_range(). On success, stores the pfn to be > - * passed to untrack_pfn_copy(). > + * tables copied during copy_page_range(). Will store the pfn to be > + * passed to untrack_pfn_copy() only if there is something to be untracked. > + * Callers should initialize the pfn to 0. > */ > static inline int track_pfn_copy(struct vm_area_struct *dst_vma, > struct vm_area_struct *src_vma, unsigned long *pfn) > @@ -1522,7 +1523,9 @@ static inline int track_pfn_copy(struct vm_area_struct *dst_vma, > > /* > * untrack_pfn_copy is called when a VM_PFNMAP VMA failed to copy during > - * copy_page_range(), but after track_pfn_copy() was already called. > + * copy_page_range(), but after track_pfn_copy() was already called. Can > + * be called even if track_pfn_copy() did not actually track anything: > + * handled internally. > */ > static inline void untrack_pfn_copy(struct vm_area_struct *dst_vma, > unsigned long pfn) > diff --git a/mm/memory.c b/mm/memory.c > index 2d8c265fc7d60..1a35165622e1c 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1361,7 +1361,7 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma) > struct mm_struct *dst_mm = dst_vma->vm_mm; > struct mm_struct *src_mm = src_vma->vm_mm; > struct mmu_notifier_range range; > - unsigned long next, pfn; > + unsigned long next, pfn = 0; > bool is_cow; > int ret; > > -- > 2.48.1 >
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