The patch titled
Subject: nios2/mm: refactor swap PTE layout
has been added to the -mm mm-unstable branch. Its filename is
nios2-mm-refactor-swap-pte-layout.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/nios2-mm-refactor-swap-pte-layout.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: nios2/mm: refactor swap PTE layout
Date: Fri, 13 Jan 2023 18:10:13 +0100
nios2 disables swap for a good reason: it doesn't even provide sufficient
type bits as required by core MM. However, swap entries are nowadays also
used for other purposes (migration entries, PTE markers, HWPoison, ...),
and accidential use could be problematic.
Let's properly use 5 bits for the swap type and document the layout. Bits
26--31 should get ignored by hardware completely, so they can be used.
Link: https://lkml.kernel.org/r/20230113171026.582290-14-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Dinh Nguyen <dinguyen@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/arch/nios2/include/asm/pgtable.h~nios2-mm-refactor-swap-pte-layout
+++ a/arch/nios2/include/asm/pgtable.h
@@ -232,19 +232,21 @@ static inline unsigned long pmd_page_vad
__FILE__, __LINE__, pgd_val(e))
/*
- * Encode and decode a swap entry (must be !pte_none(pte) && !pte_present(pte):
+ * Encode/decode swap entries and swap PTEs. Swap PTEs are all PTEs that
+ * are !pte_none() && !pte_present().
*
- * 31 30 29 28 27 26 25 24 23 22 21 20 19 18 ... 1 0
- * 0 0 0 0 type. 0 0 0 0 0 0 offset.........
+ * Format of swap PTEs:
*
- * This gives us up to 2**2 = 4 swap files and 2**20 * 4K = 4G per swap file.
+ * 3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1
+ * 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+ * 0 < type -> 0 0 0 0 0 0 <-------------- offset --------------->
*
- * Note that the offset field is always non-zero, thus !pte_none(pte) is always
- * true.
+ * Note that the offset field is always non-zero if the swap type is 0, thus
+ * !pte_none() is always true.
*/
-#define __swp_type(swp) (((swp).val >> 26) & 0x3)
+#define __swp_type(swp) (((swp).val >> 26) & 0x1f)
#define __swp_offset(swp) ((swp).val & 0xfffff)
-#define __swp_entry(type, off) ((swp_entry_t) { (((type) & 0x3) << 26) \
+#define __swp_entry(type, off) ((swp_entry_t) { (((type) & 0x1f) << 26) \
| ((off) & 0xfffff) })
#define __swp_entry_to_pte(swp) ((pte_t) { (swp).val })
#define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val(pte) })
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-userfaultfd-rely-on-vma-vm_page_prot-in-uffd_wp_range.patch
mm-userfaultfd-rely-on-vma-vm_page_prot-in-uffd_wp_range-fix.patch
mm-mprotect-drop-pgprot_t-parameter-from-change_protection.patch
mm-mprotect-drop-pgprot_t-parameter-from-change_protection-fix.patch
selftests-vm-cow-add-cow-tests-for-collapsing-of-pte-mapped-anon-thp.patch
mm-nommu-factor-out-check-for-nommu-shared-mappings-into-is_nommu_shared_mapping.patch
mm-nommu-dont-use-vm_mayshare-for-map_private-mappings.patch
drivers-misc-open-dice-dont-touch-vm_mayshare.patch
selftests-mm-define-madv_pageout-to-fix-compilation-issues.patch
mm-debug_vm_pgtable-more-pte_swp_exclusive-sanity-checks.patch
alpha-mm-support-__have_arch_pte_swp_exclusive.patch
arc-mm-support-__have_arch_pte_swp_exclusive.patch
arm-mm-support-__have_arch_pte_swp_exclusive.patch
csky-mm-support-__have_arch_pte_swp_exclusive.patch
hexagon-mm-support-__have_arch_pte_swp_exclusive.patch
ia64-mm-support-__have_arch_pte_swp_exclusive.patch
loongarch-mm-support-__have_arch_pte_swp_exclusive.patch
m68k-mm-remove-dummy-__swp-definitions-for-nommu.patch
m68k-mm-support-__have_arch_pte_swp_exclusive.patch
microblaze-mm-support-__have_arch_pte_swp_exclusive.patch
mips-mm-support-__have_arch_pte_swp_exclusive.patch
nios2-mm-refactor-swap-pte-layout.patch
nios2-mm-support-__have_arch_pte_swp_exclusive.patch
openrisc-mm-support-__have_arch_pte_swp_exclusive.patch
parisc-mm-support-__have_arch_pte_swp_exclusive.patch
powerpc-mm-support-__have_arch_pte_swp_exclusive-on-32bit-book3s.patch
powerpc-nohash-mm-support-__have_arch_pte_swp_exclusive.patch
riscv-mm-support-__have_arch_pte_swp_exclusive.patch
sh-mm-support-__have_arch_pte_swp_exclusive.patch
sparc-mm-support-__have_arch_pte_swp_exclusive-on-32bit.patch
sparc-mm-support-__have_arch_pte_swp_exclusive-on-64bit.patch
um-mm-support-__have_arch_pte_swp_exclusive.patch
x86-mm-support-__have_arch_pte_swp_exclusive-also-on-32bit.patch
xtensa-mm-support-__have_arch_pte_swp_exclusive.patch
mm-remove-__have_arch_pte_swp_exclusive.patch
