arm64: Ignore hardware dirty bit updates in ptep_set_wrprotect()
ptep_set_wrprotect() is only called on CoW mappings which are private (!VM_SHARED) with the pte either read-only (!PTE_WRITE && PTE_RDONLY) or writable and software-dirty (PTE_WRITE && !PTE_RDONLY && PTE_DIRTY). There is no race with the hardware update of the dirty state: clearing of PTE_RDONLY when PTE_WRITE (a.k.a. PTE_DBM) is set. This patch removes the code setting the software PTE_DIRTY bit in ptep_set_wrprotect() as superfluous. A VM_WARN_ONCE is introduced in case the above logic is wrong or the core mm code changes its use of ptep_set_wrprotect(). Reviewed-by: Will Deacon <will.deacon@arm.com> Acked-by: Steve Capper <steve.capper@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
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1 changed files with 13 additions and 8 deletions
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@ -634,23 +634,28 @@ static inline pmd_t pmdp_huge_get_and_clear(struct mm_struct *mm,
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#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
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/*
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* ptep_set_wrprotect - mark read-only while trasferring potential hardware
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* dirty status (PTE_DBM && !PTE_RDONLY) to the software PTE_DIRTY bit.
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* ptep_set_wrprotect - mark read-only while preserving the hardware update of
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* the Access Flag.
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*/
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#define __HAVE_ARCH_PTEP_SET_WRPROTECT
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static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long address, pte_t *ptep)
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{
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pte_t old_pte, pte;
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/*
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* ptep_set_wrprotect() is only called on CoW mappings which are
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* private (!VM_SHARED) with the pte either read-only (!PTE_WRITE &&
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* PTE_RDONLY) or writable and software-dirty (PTE_WRITE &&
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* !PTE_RDONLY && PTE_DIRTY); see is_cow_mapping() and
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* protection_map[]. There is no race with the hardware update of the
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* dirty state: clearing of PTE_RDONLY when PTE_WRITE (a.k.a. PTE_DBM)
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* is set.
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*/
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VM_WARN_ONCE(pte_write(*ptep) && !pte_dirty(*ptep),
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"%s: potential race with hardware DBM", __func__);
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pte = READ_ONCE(*ptep);
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do {
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old_pte = pte;
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/*
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* If hardware-dirty (PTE_WRITE/DBM bit set and PTE_RDONLY
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* clear), set the PTE_DIRTY bit.
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*/
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if (pte_hw_dirty(pte))
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pte = pte_mkdirty(pte);
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pte = pte_wrprotect(pte);
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pte_val(pte) = cmpxchg_relaxed(&pte_val(*ptep),
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pte_val(old_pte), pte_val(pte));
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