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s390/pgtable: cleanup description of swp pte layout

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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.

Link: https://lkml.kernel.org/r/20220329164329.208407-6-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2022-05-09 18:20:46 -07:00 committed by akpm
parent 570ef36350
commit 8043d26c46
1 changed files with 8 additions and 9 deletions
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17
arch/s390/include/asm/pgtable.h
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@ -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)