The patch titled
Subject: mm/swap: fix SWP_PFN_BITS with CONFIG_PHYS_ADDR_T_64BIT on 32bit
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-swap-fix-swp_pfn_bits-with-config_phys_addr_t_64bit-on-32bit.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swap-fix-swp_pfn_bits-with-config_phys_addr_t_64bit-on-32bit.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm/swap: fix SWP_PFN_BITS with CONFIG_PHYS_ADDR_T_64BIT on 32bit
Date: Mon, 5 Dec 2022 16:08:57 +0100
We use "unsigned long" to store a PFN in the kernel and phys_addr_t to
store a physical address.
On a 64bit system, both are 64bit wide. However, on a 32bit system, the
latter might be 64bit wide. This is, for example, the case on x86 with
PAE: phys_addr_t and PTEs are 64bit wide, while "unsigned long" only
spans 32bit.
The current definition of SWP_PFN_BITS without MAX_PHYSMEM_BITS misses
that case, and assumes that the maximum PFN is limited by a 32bit
phys_addr_t. This implies, that SWP_PFN_BITS will currently only be able
to cover 4 GiB - 1 on any 32bit system, which is wrong. We can end up
masking off valid PFN bits from the swap offset.
Ideally, we'd use something like "sizeof(phys_addr_t) * 8 - PAGE_SHIFT",
however, we might exceed SWP_TYPE_SHIFT and make the BUILD_BUG_ON() in
is_pfn_swap_entry() unhappy. Note that swp_entry_t is effectively an
unsigned long.
Consequently, simply rely on SWP_TYPE_SHIFT in case we're on 32bit and
CONFIG_PHYS_ADDR_T_64BIT is defined.
For example, on an 8 GiB x86 PAE system, we currently fail removing
migration entries (remove_migration_ptes()) that target PFNs above 4 GiB,
because mm/page_vma_mapped.c:check_pte() will fail to identify a PFN match
as swp_offset_pfn() wrongly masks off valid PFN bits.
With THP, split_huge_page_to_list()->...->remap_page() will leave
migration entries in place and continue to unlock the page, which is
wrong. Later, when we stumble over these migration entries (e.g., via
/proc/self/pagemap), pfn_swap_entry_to_page() will BUG_ON() because these
migration entries shouldn't exist anymore and the page was unlocked.
[ 33.067591] kernel BUG at include/linux/swapops.h:497!
[ 33.067597] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
[ 33.067602] CPU: 3 PID: 742 Comm: cow Tainted: G E 6.1.0-rc8+ #16
[ 33.067605] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-1.fc36 04/01/2014
[ 33.067606] EIP: pagemap_pmd_range+0x644/0x650
[ 33.067612] Code: 00 00 00 00 66 90 89 ce b9 00 f0 ff ff e9 ff fb ...
[ 33.067615] EAX: ee394000 EBX: 00000002 ECX: ee394000 EDX: 00000000
[ 33.067617] ESI: c1b0ded4 EDI: 00024a00 EBP: c1b0ddb4 ESP: c1b0dd68
[ 33.067619] DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068 EFLAGS: 00010246
[ 33.067624] CR0: 80050033 CR2: b7a00000 CR3: 01bbbd20 CR4: 00350ef0
[ 33.067625] Call Trace:
[ 33.067628] ? madvise_free_pte_range+0x720/0x720
[ 33.067632] ? smaps_pte_range+0x4b0/0x4b0
[ 33.067634] walk_pgd_range+0x325/0x720
[ 33.067637] ? mt_find+0x1d6/0x3a0
[ 33.067641] ? mt_find+0x1d6/0x3a0
[ 33.067643] __walk_page_range+0x164/0x170
[ 33.067646] walk_page_range+0xf9/0x170
[ 33.067648] ? __kmem_cache_alloc_node+0x2a8/0x340
[ 33.067653] pagemap_read+0x124/0x280
[ 33.067658] ? default_llseek+0x101/0x160
[ 33.067662] ? smaps_account+0x1d0/0x1d0
[ 33.067664] vfs_read+0x90/0x290
[ 33.067667] ? do_madvise.part.0+0x24b/0x390
[ 33.067669] ? debug_smp_processor_id+0x12/0x20
[ 33.067673] ksys_pread64+0x58/0x90
[ 33.067675] __ia32_sys_ia32_pread64+0x1b/0x20
[ 33.067680] __do_fast_syscall_32+0x4c/0xc0
[ 33.067683] do_fast_syscall_32+0x29/0x60
[ 33.067686] do_SYSENTER_32+0x15/0x20
[ 33.067689] entry_SYSENTER_32+0x98/0xf1
Link: https://lkml.kernel.org/r/20221205150857.167583-1-david@xxxxxxxxxx
Fixes: 0d206b5d2e0d ("mm/swap: add swp_offset_pfn() to fetch PFN from swap entry")
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/swapops.h | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
--- a/include/linux/swapops.h~mm-swap-fix-swp_pfn_bits-with-config_phys_addr_t_64bit-on-32bit
+++ a/include/linux/swapops.h
@@ -32,11 +32,13 @@
* store PFN, we only need SWP_PFN_BITS bits. Each of the pfn swap entries
* can use the extra bits to store other information besides PFN.
*/
-#ifdef MAX_PHYSMEM_BITS
+#if defined(MAX_PHYSMEM_BITS)
#define SWP_PFN_BITS (MAX_PHYSMEM_BITS - PAGE_SHIFT)
-#else /* MAX_PHYSMEM_BITS */
+#elif !defined(CONFIG_64BIT) && defined(CONFIG_PHYS_ADDR_T_64BIT)
+#define SWP_PFN_BITS SWP_TYPE_SHIFT
+#else
#define SWP_PFN_BITS (BITS_PER_LONG - PAGE_SHIFT)
-#endif /* MAX_PHYSMEM_BITS */
+#endif /* defined(MAX_PHYSMEM_BITS) */
#define SWP_PFN_MASK (BIT(SWP_PFN_BITS) - 1)
/**
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-swap-fix-swp_pfn_bits-with-config_phys_addr_t_64bit-on-32bit.patch
selftests-vm-add-ksm-unmerge-tests.patch
mm-pagewalk-dont-trigger-test_walk-in-walk_page_vma.patch
selftests-vm-add-test-to-measure-madv_unmergeable-performance.patch
mm-ksm-simplify-break_ksm-to-not-rely-on-vm_fault_write.patch
mm-remove-vm_fault_write.patch
mm-ksm-fix-ksm-cow-breaking-with-userfaultfd-wp-via-fault_flag_unshare.patch
mm-pagewalk-add-walk_page_range_vma.patch
mm-ksm-convert-break_ksm-to-use-walk_page_range_vma.patch
mm-gup-remove-foll_migration.patch
