| Message ID | 20220329164329.208407-6-david@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: COW fixes part 3: reliable GUP R/W FOLL_GET of anonymous pages | expand |
On Tue, 29 Mar 2022 18:43:26 +0200 David Hildenbrand <david@redhat.com> wrote: > Bit 52 and bit 55 don't have to be zero: they only trigger a > translation-specifiation exception if the PTE is marked as valid, which > is not the case for swap ptes. > > Document which bits are used for what, and which ones are unused. > > Signed-off-by: David Hildenbrand <david@redhat.com> > --- > arch/s390/include/asm/pgtable.h | 17 ++++++++--------- > 1 file changed, 8 insertions(+), 9 deletions(-) > > diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h > index 9df679152620..3982575bb586 100644 > --- a/arch/s390/include/asm/pgtable.h > +++ b/arch/s390/include/asm/pgtable.h > @@ -1712,18 +1712,17 @@ static inline int has_transparent_hugepage(void) > /* > * 64 bit swap entry format: > * A page-table entry has some bits we have to treat in a special way. > - * Bits 52 and bit 55 have to be zero, otherwise a specification > - * exception will occur instead of a page translation exception. The > - * specification exception has the bad habit not to store necessary > - * information in the lowcore. > - * Bits 54 and 63 are used to indicate the page type. > + * Bits 54 and 63 are used to indicate the page type. Bit 53 marks the pte > + * as invalid. > * A swap pte is indicated by bit pattern (pte & 0x201) == 0x200 > - * This leaves the bits 0-51 and bits 56-62 to store type and offset. > - * We use the 5 bits from 57-61 for the type and the 52 bits from 0-51 > - * for the offset. > - * | offset |01100|type |00| > + * | offset |X11XX|type |S0| > * |0000000000111111111122222222223333333333444444444455|55555|55566|66| > * |0123456789012345678901234567890123456789012345678901|23456|78901|23| > + * > + * Bits 0-51 store the offset. > + * Bits 57-61 store the type. > + * Bit 62 (S) is used for softdirty tracking. > + * Bits 52, 55 and 56 (X) are unused. > */ > > #define __SWP_OFFSET_MASK ((1UL << 52) - 1) Thanks David! Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h index 9df679152620..3982575bb586 100644 --- a/arch/s390/include/asm/pgtable.h +++ b/arch/s390/include/asm/pgtable.h @@ -1712,18 +1712,17 @@ static inline int has_transparent_hugepage(void) /* * 64 bit swap entry format: * A page-table entry has some bits we have to treat in a special way. - * Bits 52 and bit 55 have to be zero, otherwise a specification - * exception will occur instead of a page translation exception. The - * specification exception has the bad habit not to store necessary - * information in the lowcore. - * Bits 54 and 63 are used to indicate the page type. + * Bits 54 and 63 are used to indicate the page type. Bit 53 marks the pte + * as invalid. * A swap pte is indicated by bit pattern (pte & 0x201) == 0x200 - * This leaves the bits 0-51 and bits 56-62 to store type and offset. - * We use the 5 bits from 57-61 for the type and the 52 bits from 0-51 - * for the offset. - * | offset |01100|type |00| + * | offset |X11XX|type |S0| * |0000000000111111111122222222223333333333444444444455|55555|55566|66| * |0123456789012345678901234567890123456789012345678901|23456|78901|23| + * + * Bits 0-51 store the offset. + * Bits 57-61 store the type. + * Bit 62 (S) is used for softdirty tracking. + * Bits 52, 55 and 56 (X) are unused. */ #define __SWP_OFFSET_MASK ((1UL << 52) - 1)
Bit 52 and bit 55 don't have to be zero: they only trigger a translation-specifiation exception if the PTE is marked as valid, which is not the case for swap ptes. Document which bits are used for what, and which ones are unused. Signed-off-by: David Hildenbrand <david@redhat.com> --- arch/s390/include/asm/pgtable.h | 17 ++++++++--------- 1 file changed, 8 insertions(+), 9 deletions(-)