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=-13.6 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 1DAD1C433E2 for ; Wed, 2 Sep 2020 03:56:31 +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 7CF96206EB for ; Wed, 2 Sep 2020 03:56:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7CF96206EB 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 bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4Bh9984Nb7zDqWn for ; Wed, 2 Sep 2020 13:56:28 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) 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 4Bh91w3yZfzDqfH for ; Wed, 2 Sep 2020 13:50:11 +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 033D3D6E; Tue, 1 Sep 2020 20:50:10 -0700 (PDT) Received: from [192.168.0.130] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 200CE3F66F; Tue, 1 Sep 2020 20:50:04 -0700 (PDT) From: Anshuman Khandual Subject: Re: [PATCH v3 13/13] mm/debug_vm_pgtable: populate a pte entry before fetching it To: "Aneesh Kumar K.V" , linux-mm@kvack.org, akpm@linux-foundation.org References: <20200827080438.315345-1-aneesh.kumar@linux.ibm.com> <20200827080438.315345-14-aneesh.kumar@linux.ibm.com> <7ef7c302-e7e6-570e-3100-5dd1bf9551be@linux.ibm.com> Message-ID: <4ba15b8f-ac90-17ec-9b95-0451e2a38e98@arm.com> Date: Wed, 2 Sep 2020 09:19:28 +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: <7ef7c302-e7e6-570e-3100-5dd1bf9551be@linux.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit 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: linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, Christophe Leroy , x86@kernel.org, Mike Rapoport , Qian Cai , Gerald Schaefer , Vineet Gupta , linux-snps-arc@lists.infradead.org, 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 09/01/2020 03:28 PM, Aneesh Kumar K.V wrote: > On 9/1/20 1:08 PM, Anshuman Khandual wrote: >> >> >> On 09/01/2020 12:07 PM, Aneesh Kumar K.V wrote: >>> On 9/1/20 8:55 AM, Anshuman Khandual wrote: >>>> >>>> >>>> On 08/27/2020 01:34 PM, Aneesh Kumar K.V wrote: >>>>> pte_clear_tests operate on an existing pte entry. Make sure that is not a none >>>>> pte entry. >>>>> >>>>> Signed-off-by: Aneesh Kumar K.V >>>>> --- >>>>>    mm/debug_vm_pgtable.c | 6 ++++-- >>>>>    1 file changed, 4 insertions(+), 2 deletions(-) >>>>> >>>>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c >>>>> index 21329c7d672f..8527ebb75f2c 100644 >>>>> --- a/mm/debug_vm_pgtable.c >>>>> +++ b/mm/debug_vm_pgtable.c >>>>> @@ -546,7 +546,7 @@ static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp, >>>>>    static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep, >>>>>                       unsigned long vaddr) >>>>>    { >>>>> -    pte_t pte = ptep_get(ptep); >>>>> +    pte_t pte =  ptep_get_and_clear(mm, vaddr, ptep); >>>> >>>> Seems like ptep_get_and_clear() here just clears the entry in preparation >>>> for a following set_pte_at() which otherwise would have been a problem on >>>> ppc64 as you had pointed out earlier i.e set_pte_at() should not update an >>>> existing valid entry. So the commit message here is bit misleading. >>>> >>> >>> and also fetch the pte value which is used further. >>> >>> >>>>>          pr_debug("Validating PTE clear\n"); >>>>>        pte = __pte(pte_val(pte) | RANDOM_ORVALUE); >>>>> @@ -944,7 +944,7 @@ static int __init debug_vm_pgtable(void) >>>>>        p4d_t *p4dp, *saved_p4dp; >>>>>        pud_t *pudp, *saved_pudp; >>>>>        pmd_t *pmdp, *saved_pmdp, pmd; >>>>> -    pte_t *ptep; >>>>> +    pte_t *ptep, pte; >>>>>        pgtable_t saved_ptep; >>>>>        pgprot_t prot, protnone; >>>>>        phys_addr_t paddr; >>>>> @@ -1049,6 +1049,8 @@ static int __init debug_vm_pgtable(void) >>>>>         */ >>>>>          ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl); >>>>> +    pte = pfn_pte(pte_aligned, prot); >>>>> +    set_pte_at(mm, vaddr, ptep, pte); >>>> >>>> Not here, creating and populating an entry must be done in respective >>>> test functions itself. Besides, this seems bit redundant as well. The >>>> test pte_clear_tests() with the above change added, already >>>> >>>> - Clears the PTEP entry with ptep_get_and_clear() >>> >>> and fetch the old value set previously. >> >> In that case, please move above two lines i.e >> >> pte = pfn_pte(pte_aligned, prot); >> set_pte_at(mm, vaddr, ptep, pte); >> >> from debug_vm_pgtable() to pte_clear_tests() and update it's arguments >> as required. >> > > Frankly, I don't understand what these tests are testing. It all looks like some random clear and set. The idea here is to have some value with some randomness preferably, in a given PTEP before attempting to clear the entry, in order to make sure that pte_clear() is indeed clearing something of non-zero value. > > static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep, >                    unsigned long vaddr, unsigned long pfn, >                    pgprot_t prot) > { > >     pte_t pte = pfn_pte(pfn, prot); >     set_pte_at(mm, vaddr, ptep, pte); > >     pte =  ptep_get_and_clear(mm, vaddr, ptep); Looking at this again, this preceding pfn_pte() followed by set_pte_at() is not really required. Its reasonable to start with what ever was there in the PTEP as a seed value which anyway gets added with RANDOM_ORVALUE. s/ptep_get/ptep_get_and_clear is sufficient to take care of the powerpc set_pte_at() constraint.