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Date: Wed, 07 Jun 2017 16:32:28 +0100 From: Punit Agrawal <punit.agrawal@....com> To: Will Deacon <will.deacon@....com> Cc: Catalin Marinas <catalin.marinas@....com>, David Woods <dwoods@...lanox.com>, steve.capper@....com, tbaicar@...eaurora.org, linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, manoj.iyer@...onical.com Subject: Re: [PATCH v2 1/3] arm64: hugetlb: Fix huge_pte_offset to return poisoned page table entries Will Deacon <will.deacon@....com> writes: > On Wed, Jun 07, 2017 at 03:30:37PM +0100, Catalin Marinas wrote: >> On Wed, Jun 07, 2017 at 02:47:32PM +0100, Will Deacon wrote: >> > On Wed, May 17, 2017 at 04:23:34PM +0100, Punit Agrawal wrote: >> > > --- a/arch/arm64/mm/hugetlbpage.c >> > > +++ b/arch/arm64/mm/hugetlbpage.c >> > > @@ -136,36 +136,27 @@ pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr) >> > > { >> > > pgd_t *pgd; >> > > pud_t *pud; >> > > - pmd_t *pmd = NULL; >> > > - pte_t *pte = NULL; >> > > + pmd_t *pmd; >> > > >> > > pgd = pgd_offset(mm, addr); >> > > pr_debug("%s: addr:0x%lx pgd:%p\n", __func__, addr, pgd); >> > > if (!pgd_present(*pgd)) >> > > return NULL; >> > > + >> > > pud = pud_offset(pgd, addr); >> > > - if (!pud_present(*pud)) >> > > + if (pud_none(*pud)) >> > > return NULL; >> > >> > Do you actually need this special case? >> > >> > > - >> > > - if (pud_huge(*pud)) >> > > + /* swap or huge page */ >> > > + if (!pud_present(*pud) || pud_huge(*pud)) >> > >> > ... couldn't you just add a '|| pud_none(*pud)' in here? >> > I think an earlier version took this approach but... >> > > return (pte_t *)pud; >> >> But then you no longer return NULL if *pud == 0. > > Does that actually matter? The bits of hugetlb code I looked at will > deferenced the returned pud and handle the huge_pte_none case correctly. For hugetlb fault handling (hugetlb_fault()), returning NULL vs pointer to the pud/pmd results in different behaviour. If we return the pud when pud_none(), then we lose the resulting hugepage size check we get from huge_pte_alloc(). > > Will
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