From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5334FC43613 for ; Mon, 24 Jun 2019 06:54:46 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A0B3220679 for ; Mon, 24 Jun 2019 06:54:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A0B3220679 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 45XKm25tRyzDqDY for ; Mon, 24 Jun 2019 16:54:42 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=arm.com (client-ip=217.140.110.172; helo=foss.arm.com; envelope-from=anshuman.khandual@arm.com; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=arm.com Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lists.ozlabs.org (Postfix) with ESMTP id 45XKjl4lFDzDqB9 for ; Mon, 24 Jun 2019 16:52:41 +1000 (AEST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7C6152B; Sun, 23 Jun 2019 23:52:38 -0700 (PDT) Received: from [10.162.41.123] (p8cg001049571a15.blr.arm.com [10.162.41.123]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 61E2B3F246; Sun, 23 Jun 2019 23:54:24 -0700 (PDT) Subject: Re: [PATCH 3/3] mm/vmalloc: fix vmalloc_to_page for huge vmap mappings To: Nicholas Piggin , linux-mm@kvack.org References: <20190623094446.28722-1-npiggin@gmail.com> <20190623094446.28722-4-npiggin@gmail.com> From: Anshuman Khandual Message-ID: <8668f76d-faad-4e57-2f7b-f2b8969b1026@arm.com> Date: Mon, 24 Jun 2019 12:22:59 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190623094446.28722-4-npiggin@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Ard Biesheuvel , Andrew Morton , linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 06/23/2019 03:14 PM, Nicholas Piggin wrote: > vmalloc_to_page returns NULL for addresses mapped by larger pages[*]. > Whether or not a vmap is huge depends on the architecture details, > alignments, boot options, etc., which the caller can not be expected > to know. Therefore HUGE_VMAP is a regression for vmalloc_to_page. > > This change teaches vmalloc_to_page about larger pages, and returns > the struct page that corresponds to the offset within the large page. > This makes the API agnostic to mapping implementation details. > > [*] As explained by commit 029c54b095995 ("mm/vmalloc.c: huge-vmap: > fail gracefully on unexpected huge vmap mappings") > > Signed-off-by: Nicholas Piggin > --- > include/asm-generic/4level-fixup.h | 1 + > include/asm-generic/5level-fixup.h | 1 + > mm/vmalloc.c | 37 +++++++++++++++++++----------- > 3 files changed, 26 insertions(+), 13 deletions(-) > > diff --git a/include/asm-generic/4level-fixup.h b/include/asm-generic/4level-fixup.h > index e3667c9a33a5..3cc65a4dd093 100644 > --- a/include/asm-generic/4level-fixup.h > +++ b/include/asm-generic/4level-fixup.h > @@ -20,6 +20,7 @@ > #define pud_none(pud) 0 > #define pud_bad(pud) 0 > #define pud_present(pud) 1 > +#define pud_large(pud) 0 > #define pud_ERROR(pud) do { } while (0) > #define pud_clear(pud) pgd_clear(pud) > #define pud_val(pud) pgd_val(pud) > diff --git a/include/asm-generic/5level-fixup.h b/include/asm-generic/5level-fixup.h > index bb6cb347018c..c4377db09a4f 100644 > --- a/include/asm-generic/5level-fixup.h > +++ b/include/asm-generic/5level-fixup.h > @@ -22,6 +22,7 @@ > #define p4d_none(p4d) 0 > #define p4d_bad(p4d) 0 > #define p4d_present(p4d) 1 > +#define p4d_large(p4d) 0 > #define p4d_ERROR(p4d) do { } while (0) > #define p4d_clear(p4d) pgd_clear(p4d) > #define p4d_val(p4d) pgd_val(p4d) > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 4c9e150e5ad3..4be98f700862 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -36,6 +36,7 @@ > #include > > #include > +#include > #include > #include > > @@ -284,26 +285,36 @@ struct page *vmalloc_to_page(const void *vmalloc_addr) > > if (pgd_none(*pgd)) > return NULL; > + > p4d = p4d_offset(pgd, addr); > if (p4d_none(*p4d)) > return NULL; > - pud = pud_offset(p4d, addr); > + if (WARN_ON_ONCE(p4d_bad(*p4d))) > + return NULL; The warning here is a required addition but it needs to be moved after p4d_large() check. Please see the next comment below. > +#ifdef CONFIG_HAVE_ARCH_HUGE_VMAP > + if (p4d_large(*p4d)) > + return p4d_page(*p4d) + ((addr & ~P4D_MASK) >> PAGE_SHIFT); > +#endif > > - /* > - * Don't dereference bad PUD or PMD (below) entries. This will also > - * identify huge mappings, which we may encounter on architectures > - * that define CONFIG_HAVE_ARCH_HUGE_VMAP=y. Such regions will be > - * identified as vmalloc addresses by is_vmalloc_addr(), but are > - * not [unambiguously] associated with a struct page, so there is > - * no correct value to return for them. > - */ > - WARN_ON_ONCE(pud_bad(*pud)); > - if (pud_none(*pud) || pud_bad(*pud)) > + pud = pud_offset(p4d, addr); > + if (pud_none(*pud)) > + return NULL; > + if (WARN_ON_ONCE(pud_bad(*pud))) > return NULL; > +#ifdef CONFIG_HAVE_ARCH_HUGE_VMAP > + if (pud_large(*pud)) > + return pud_page(*pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT); > +#endif > + pud_bad() on arm64 returns true when the PUD does not point to a next page table page implying the fact that it might be a large/huge entry. I am not sure if the semantics holds good for other architectures too. But on arm64 if pud_large() is true, then pud_bad() will be true as well. So pud_bad() check must happen after pud_large() check. So the sequence here should be 1. pud_none() --> Nothing is in here, return NULL 2. pud_large() --> Return offset page address from the huge page mapping 3. pud_bad() --> Return NULL as there is no more page table level left Checking pud_bad() first can return NULL for a valid huge mapping. > pmd = pmd_offset(pud, addr); > - WARN_ON_ONCE(pmd_bad(*pmd)); > - if (pmd_none(*pmd) || pmd_bad(*pmd)) > + if (pmd_none(*pmd)) > + return NULL; > + if (WARN_ON_ONCE(pmd_bad(*pmd))) > return NULL; > +#ifdef CONFIG_HAVE_ARCH_HUGE_VMAP > + if (pmd_large(*pmd)) > + return pmd_page(*pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT); > +#endif Ditto. I see that your previous proposal had this right which got changed in this manner after my comments. Sorry about it. It was recently when I learned (correctly) that expected semantics of pxx_bad() is that - It does not point to the next page table page. Hence I wonder why is this not renamed as pxx_table() instead to make it absolutely clear.