Messages in this thread Patch in this message |  | | From | David Hildenbrand <> | | Subject | [PATCH v2] x86/mm/pat: (un)track_pfn_copy() fix + doc improvements | | Date | Tue, 8 Apr 2025 10:59:50 +0200 |
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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 :) * 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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