On Mon, Jan 29, 2024 at 01:46:35PM +0100, David Hildenbrand wrote: > From: Ryan Roberts <ryan.roberts@xxxxxxx> > > Since the high bits [51:48] of an OA are not stored contiguously in the > PTE, there is a theoretical bug in set_ptes(), which just adds PAGE_SIZE > to the pte to get the pte with the next pfn. This works until the pfn > crosses the 48-bit boundary, at which point we overflow into the upper > attributes. > > Of course one could argue (and Matthew Wilcox has :) that we will never > see a folio cross this boundary because we only allow naturally aligned > power-of-2 allocation, so this would require a half-petabyte folio. So > its only a theoretical bug. But its better that the code is robust > regardless. > > I've implemented pte_next_pfn() as part of the fix, which is an opt-in > core-mm interface. So that is now available to the core-mm, which will > be needed shortly to support forthcoming fork()-batching optimizations. > > Link: https://lkml.kernel.org/r/20240125173534.1659317-1-ryan.roberts@xxxxxxx > Fixes: 4a169d61c2ed ("arm64: implement the new page table range API") > Closes: https://lore.kernel.org/linux-mm/fdaeb9a5-d890-499a-92c8-d171df43ad01@xxxxxxx/ > Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> > Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx> > Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> Reviewed-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx> > --- > arch/arm64/include/asm/pgtable.h | 28 +++++++++++++++++----------- > 1 file changed, 17 insertions(+), 11 deletions(-) > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index b50270107e2f..9428801c1040 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -341,6 +341,22 @@ static inline void __sync_cache_and_tags(pte_t pte, unsigned int nr_pages) > mte_sync_tags(pte, nr_pages); > } > > +/* > + * Select all bits except the pfn > + */ > +static inline pgprot_t pte_pgprot(pte_t pte) > +{ > + unsigned long pfn = pte_pfn(pte); > + > + return __pgprot(pte_val(pfn_pte(pfn, __pgprot(0))) ^ pte_val(pte)); > +} > + > +#define pte_next_pfn pte_next_pfn > +static inline pte_t pte_next_pfn(pte_t pte) > +{ > + return pfn_pte(pte_pfn(pte) + 1, pte_pgprot(pte)); > +} > + > static inline void set_ptes(struct mm_struct *mm, > unsigned long __always_unused addr, > pte_t *ptep, pte_t pte, unsigned int nr) > @@ -354,7 +370,7 @@ static inline void set_ptes(struct mm_struct *mm, > if (--nr == 0) > break; > ptep++; > - pte_val(pte) += PAGE_SIZE; > + pte = pte_next_pfn(pte); > } > } > #define set_ptes set_ptes > @@ -433,16 +449,6 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte) > return clear_pte_bit(pte, __pgprot(PTE_SWP_EXCLUSIVE)); > } > > -/* > - * Select all bits except the pfn > - */ > -static inline pgprot_t pte_pgprot(pte_t pte) > -{ > - unsigned long pfn = pte_pfn(pte); > - > - return __pgprot(pte_val(pfn_pte(pfn, __pgprot(0))) ^ pte_val(pte)); > -} > - > #ifdef CONFIG_NUMA_BALANCING > /* > * See the comment in include/linux/pgtable.h > -- > 2.43.0 > > -- Sincerely yours, Mike.
