fba88ede6a
This is a preparation for enabling THP migration.
As the commit b65399f6111b("arm64/mm: Change THP helpers
to comply with generic MM semantics") mentioned, pmd_present()
and pmd_trans_huge() are expected to behave in the following
manner:
-------------------------------------------------------------------------
| PMD states | pmd_present | pmd_trans_huge |
-------------------------------------------------------------------------
| Mapped | Yes | Yes |
-------------------------------------------------------------------------
| Splitting | Yes | Yes |
-------------------------------------------------------------------------
| Migration/Swap | No | No |
-------------------------------------------------------------------------
At present the PROT_NONE bit reuses the READ bit could not comply with
above semantics with two problems:
1. When splitting a PMD THP, PMD is first invalidated with
pmdp_invalidate()->pmd_mkinvalid(), which clears the PRESENT bit
and PROT_NONE bit/READ bit, if the PMD is read-only, then the PAGE_LEAF
property is also cleared, which results in pmd_present() return false.
2. When migrating, the swap entry only clear the PRESENT bit
and PROT_NONE bit/READ bit, the W/X bit may be set, so _PAGE_LEAF may be
true which results in pmd_present() return true.
Solution:
Adjust PROT_NONE bit from READ to GLOBAL bit can satisfy the above rules:
1. GLOBAL bit has no other meanings, not like the R/W/X bit, which is
also relative with _PAGE_LEAF property.
2. GLOBAL bit is at bit 5, making swap entry start from bit 6, bit 0-5
are zero, which means the PRESENT, PROT_NONE, and PAGE_LEAF are
all false, then the pmd_present() and pmd_trans_huge() return false when
in migration/swap.
Signed-off-by: Nanyong Sun <sunnanyong@huawei.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
48 lines
1.5 KiB
C
48 lines
1.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Copyright (C) 2012 Regents of the University of California
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*/
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#ifndef _ASM_RISCV_PGTABLE_BITS_H
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#define _ASM_RISCV_PGTABLE_BITS_H
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/*
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* PTE format:
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* | XLEN-1 10 | 9 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0
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* PFN reserved for SW D A G U X W R V
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*/
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#define _PAGE_ACCESSED_OFFSET 6
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#define _PAGE_PRESENT (1 << 0)
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#define _PAGE_READ (1 << 1) /* Readable */
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#define _PAGE_WRITE (1 << 2) /* Writable */
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#define _PAGE_EXEC (1 << 3) /* Executable */
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#define _PAGE_USER (1 << 4) /* User */
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#define _PAGE_GLOBAL (1 << 5) /* Global */
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#define _PAGE_ACCESSED (1 << 6) /* Set by hardware on any access */
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#define _PAGE_DIRTY (1 << 7) /* Set by hardware on any write */
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#define _PAGE_SOFT (1 << 8) /* Reserved for software */
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#define _PAGE_SPECIAL _PAGE_SOFT
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#define _PAGE_TABLE _PAGE_PRESENT
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/*
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* _PAGE_PROT_NONE is set on not-present pages (and ignored by the hardware) to
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* distinguish them from swapped out pages
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*/
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#define _PAGE_PROT_NONE _PAGE_GLOBAL
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#define _PAGE_PFN_SHIFT 10
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/* Set of bits to preserve across pte_modify() */
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#define _PAGE_CHG_MASK (~(unsigned long)(_PAGE_PRESENT | _PAGE_READ | \
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_PAGE_WRITE | _PAGE_EXEC | \
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_PAGE_USER | _PAGE_GLOBAL))
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/*
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* when all of R/W/X are zero, the PTE is a pointer to the next level
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* of the page table; otherwise, it is a leaf PTE.
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*/
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#define _PAGE_LEAF (_PAGE_READ | _PAGE_WRITE | _PAGE_EXEC)
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#endif /* _ASM_RISCV_PGTABLE_BITS_H */
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