This is a note to let you know that I've just added the patch titled
x86/mm: Move swap offset/type up in PTE to work around erratum
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-mm-move-swap-offset-type-up-in-pte-to-work-around-erratum.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Tue Aug 14 17:08:55 CEST 2018
From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Date: Thu, 7 Jul 2016 17:19:11 -0700
Subject: x86/mm: Move swap offset/type up in PTE to work around erratum
From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
commit 00839ee3b299303c6a5e26a0a2485427a3afcbbf upstream
This erratum can result in Accessed/Dirty getting set by the hardware
when we do not expect them to be (on !Present PTEs).
Instead of trying to fix them up after this happens, we just
allow the bits to get set and try to ignore them. We do this by
shifting the layout of the bits we use for swap offset/type in
our 64-bit PTEs.
It looks like this:
bitnrs: | ... | 11| 10| 9|8|7|6|5| 4| 3|2|1|0|
names: | ... |SW3|SW2|SW1|G|L|D|A|CD|WT|U|W|P|
before: | OFFSET (9-63) |0|X|X| TYPE(1-5) |0|
after: | OFFSET (14-63) | TYPE (9-13) |0|X|X|X| X| X|X|X|0|
Note that D was already a don't care (X) even before. We just
move TYPE up and turn its old spot (which could be hit by the
A bit) into all don't cares.
We take 5 bits away from the offset, but that still leaves us
with 50 bits which lets us index into a 62-bit swapfile (4 EiB).
I think that's probably fine for the moment. We could
theoretically reclaim 5 of the bits (1, 2, 3, 4, 7) but it
doesn't gain us anything.
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Dave Hansen <dave@xxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Luis R. Rodriguez <mcgrof@xxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Toshi Kani <toshi.kani@xxxxxx>
Cc: dave.hansen@xxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: mhocko@xxxxxxxx
Link: http://lkml.kernel.org/r/20160708001911.9A3FD2B6@xxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/pgtable_64.h | 26 ++++++++++++++++++++------
1 file changed, 20 insertions(+), 6 deletions(-)
--- a/arch/x86/include/asm/pgtable_64.h
+++ b/arch/x86/include/asm/pgtable_64.h
@@ -163,18 +163,32 @@ static inline int pgd_large(pgd_t pgd) {
#define pte_offset_map(dir, address) pte_offset_kernel((dir), (address))
#define pte_unmap(pte) ((void)(pte))/* NOP */
-/* Encode and de-code a swap entry */
+/*
+ * Encode and de-code a swap entry
+ *
+ * | ... | 11| 10| 9|8|7|6|5| 4| 3|2|1|0| <- bit number
+ * | ... |SW3|SW2|SW1|G|L|D|A|CD|WT|U|W|P| <- bit names
+ * | OFFSET (14->63) | TYPE (10-13) |0|X|X|X| X| X|X|X|0| <- swp entry
+ *
+ * G (8) is aliased and used as a PROT_NONE indicator for
+ * !present ptes. We need to start storing swap entries above
+ * there. We also need to avoid using A and D because of an
+ * erratum where they can be incorrectly set by hardware on
+ * non-present PTEs.
+ */
+#define SWP_TYPE_FIRST_BIT (_PAGE_BIT_PROTNONE + 1)
#define SWP_TYPE_BITS 5
-#define SWP_OFFSET_SHIFT (_PAGE_BIT_PROTNONE + 1)
+/* Place the offset above the type: */
+#define SWP_OFFSET_FIRST_BIT (SWP_TYPE_FIRST_BIT + SWP_TYPE_BITS + 1)
#define MAX_SWAPFILES_CHECK() BUILD_BUG_ON(MAX_SWAPFILES_SHIFT > SWP_TYPE_BITS)
-#define __swp_type(x) (((x).val >> (_PAGE_BIT_PRESENT + 1)) \
+#define __swp_type(x) (((x).val >> (SWP_TYPE_FIRST_BIT)) \
& ((1U << SWP_TYPE_BITS) - 1))
-#define __swp_offset(x) ((x).val >> SWP_OFFSET_SHIFT)
+#define __swp_offset(x) ((x).val >> SWP_OFFSET_FIRST_BIT)
#define __swp_entry(type, offset) ((swp_entry_t) { \
- ((type) << (_PAGE_BIT_PRESENT + 1)) \
- | ((offset) << SWP_OFFSET_SHIFT) })
+ ((type) << (SWP_TYPE_FIRST_BIT)) \
+ | ((offset) << SWP_OFFSET_FIRST_BIT) })
#define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val((pte)) })
#define __swp_entry_to_pte(x) ((pte_t) { .pte = (x).val })
Patches currently in stable-queue which might be from dave.hansen@xxxxxxxxxxxxxxx are
queue-4.4/x86-mm-move-swap-offset-type-up-in-pte-to-work-around-erratum.patch
queue-4.4/x86-mm-fix-swap-entry-comment-and-macro.patch
queue-4.4/mm-add-vm_insert_pfn_prot.patch
