On 16.03.22 19:27, Catalin Marinas wrote: > On Tue, Mar 15, 2022 at 03:18:34PM +0100, David Hildenbrand wrote: >> diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h >> index b1e1b74d993c..62e0ebeed720 100644 >> --- a/arch/arm64/include/asm/pgtable-prot.h >> +++ b/arch/arm64/include/asm/pgtable-prot.h >> @@ -14,6 +14,7 @@ >> * Software defined PTE bits definition. >> */ >> #define PTE_WRITE (PTE_DBM) /* same as DBM (51) */ >> +#define PTE_SWP_EXCLUSIVE (_AT(pteval_t, 1) << 2) /* only for swp ptes */ > > I think we can use bit 1 here. > >> @@ -909,12 +925,13 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *vma, >> /* >> * Encode and decode a swap entry: >> * bits 0-1: present (must be zero) >> - * bits 2-7: swap type >> + * bits 2: remember PG_anon_exclusive >> + * bits 3-7: swap type >> * bits 8-57: swap offset >> * bit 58: PTE_PROT_NONE (must be zero) > > I don't remember exactly why we reserved bits 0 and 1 when, from the > hardware perspective, it's sufficient for bit 0 to be 0 and the whole > pte becomes invalid. We use bit 1 as the 'table' bit (when 0 at pmd > level, it's a huge page) but we shouldn't check for this on a swap > entry. You mean arch/arm64/include/asm/pgtable-hwdef.h:#define PTE_TABLE_BIT (_AT(pteval_t, 1) << 1) right? I wonder why it even exists, for arm64 I only spot: arch/arm64/include/asm/pgtable.h:#define pte_mkhuge(pte) (__pte(pte_val(pte) & ~PTE_TABLE_BIT)) I don't really see code that sets PTE_TABLE_BIT. Similarly, I don't see code that sets PMD_TABLE_BIT/PUD_TABLE_BIT/P4D_TABLE_BIT. Most probably setting code is not using the defines, that's why I'm not finding it. -- Thanks, David / dhildenb
