On Wed, 2020-02-26 at 13:35 -0800, Dave Hansen wrote: > On 2/5/20 10:19 AM, Yu-cheng Yu wrote: > > When Shadow Stack (SHSTK) is introduced, a R/O and Dirty PTE exists in the > > following cases: > > > > (a) A modified, copy-on-write (COW) page; > > (b) A R/O page that has been COW'ed; > > (c) A SHSTK page. [...] > > diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h > > index e647e3c75578..826823df917f 100644 > > --- a/arch/x86/include/asm/pgtable_types.h > > +++ b/arch/x86/include/asm/pgtable_types.h > > @@ -23,7 +23,8 @@ > > #define _PAGE_BIT_SOFTW2 10 /* " */ > > #define _PAGE_BIT_SOFTW3 11 /* " */ > > #define _PAGE_BIT_PAT_LARGE 12 /* On 2MB or 1GB pages */ > > -#define _PAGE_BIT_SOFTW4 58 /* available for programmer */ > > +#define _PAGE_BIT_SOFTW4 57 /* available for programmer */ > > +#define _PAGE_BIT_SOFTW5 58 /* available for programmer */ > > #define _PAGE_BIT_PKEY_BIT0 59 /* Protection Keys, bit 1/4 */ > > #define _PAGE_BIT_PKEY_BIT1 60 /* Protection Keys, bit 2/4 */ > > #define _PAGE_BIT_PKEY_BIT2 61 /* Protection Keys, bit 3/4 */ > > @@ -35,6 +36,12 @@ > > #define _PAGE_BIT_SOFT_DIRTY _PAGE_BIT_SOFTW3 /* software dirty tracking */ > > #define _PAGE_BIT_DEVMAP _PAGE_BIT_SOFTW4 > > > > +/* > > + * This bit indicates a copy-on-write page, and is different from > > + * _PAGE_BIT_SOFT_DIRTY, which tracks which pages a task writes to. > > + */ > > +#define _PAGE_BIT_DIRTY_SW _PAGE_BIT_SOFTW5 /* was written to */ > > Does it *only* indicate a copy-on-write (or copy-on-access) page? If > so, haven't we misnamed it? It indicates either a copy-on-write page or a read-only page that has been cow'ed. What about _PAGE_BIT_COW? Yu-cheng
