From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751481AbdFGPcc (ORCPT ); Wed, 7 Jun 2017 11:32:32 -0400 Received: from foss.arm.com ([217.140.101.70]:34198 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751072AbdFGPcb (ORCPT ); Wed, 7 Jun 2017 11:32:31 -0400 From: Punit Agrawal To: Will Deacon Cc: Catalin Marinas , David Woods , steve.capper@arm.com, tbaicar@codeaurora.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, manoj.iyer@canonical.com Subject: Re: [PATCH v2 1/3] arm64: hugetlb: Fix huge_pte_offset to return poisoned page table entries References: <20170517152336.6052-1-punit.agrawal@arm.com> <20170517152336.6052-2-punit.agrawal@arm.com> <20170607134731.GG30263@arm.com> <20170607143037.ovyo5pxywty2r6as@localhost> <20170607145715.GI30263@arm.com> Date: Wed, 07 Jun 2017 16:32:28 +0100 In-Reply-To: <20170607145715.GI30263@arm.com> (Will Deacon's message of "Wed, 7 Jun 2017 15:57:16 +0100") Message-ID: <87h8zr24qb.fsf@e105922-lin.cambridge.arm.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Will Deacon 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