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[217.140.110.172]) by mx.google.com with ESMTP id y9si14809797edc.211.2019.07.28.06.40.26 for ; Sun, 28 Jul 2019 06:40:27 -0700 (PDT) Received-SPF: pass (google.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) client-ip=217.140.110.172; Authentication-Results: mx.google.com; spf=pass (google.com: domain of anshuman.khandual@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=anshuman.khandual@arm.com 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 2389C344; Sun, 28 Jul 2019 06:40:26 -0700 (PDT) Received: from [10.163.1.126] (unknown [10.163.1.126]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DD10B3F71A; Sun, 28 Jul 2019 06:40:19 -0700 (PDT) Subject: Re: [PATCH v9 13/21] mm: pagewalk: Add test_p?d callbacks To: Steven Price , linux-mm@kvack.org Cc: Andy Lutomirski , Ard Biesheuvel , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Dave Hansen , Ingo Molnar , James Morse , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Peter Zijlstra , Thomas Gleixner , Will Deacon , x86@kernel.org, "H. Peter Anvin" , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Mark Rutland , "Liang, Kan" , Andrew Morton References: <20190722154210.42799-1-steven.price@arm.com> <20190722154210.42799-14-steven.price@arm.com> From: Anshuman Khandual Message-ID: Date: Sun, 28 Jul 2019 19:11:00 +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: <20190722154210.42799-14-steven.price@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 07/22/2019 09:12 PM, Steven Price wrote: > It is useful to be able to skip parts of the page table tree even when > walking without VMAs. Add test_p?d callbacks similar to test_walk but > which are called just before a table at that level is walked. If the > callback returns non-zero then the entire table is skipped. > > Signed-off-by: Steven Price > --- > include/linux/mm.h | 11 +++++++++++ > mm/pagewalk.c | 24 ++++++++++++++++++++++++ > 2 files changed, 35 insertions(+) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index b22799129128..325a1ca6f820 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1447,6 +1447,11 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma, > * value means "do page table walk over the current vma," > * and a negative one means "abort current page table walk > * right now." 1 means "skip the current vma." > + * @test_pmd: similar to test_walk(), but called for every pmd. > + * @test_pud: similar to test_walk(), but called for every pud. > + * @test_p4d: similar to test_walk(), but called for every p4d. > + * Returning 0 means walk this part of the page tables, > + * returning 1 means to skip this range. > * @mm: mm_struct representing the target process of page table walk > * @vma: vma currently walked (NULL if walking outside vmas) > * @private: private data for callbacks' usage > @@ -1471,6 +1476,12 @@ struct mm_walk { > struct mm_walk *walk); > int (*test_walk)(unsigned long addr, unsigned long next, > struct mm_walk *walk); > + int (*test_pmd)(unsigned long addr, unsigned long next, > + pmd_t *pmd_start, struct mm_walk *walk); > + int (*test_pud)(unsigned long addr, unsigned long next, > + pud_t *pud_start, struct mm_walk *walk); > + int (*test_p4d)(unsigned long addr, unsigned long next, > + p4d_t *p4d_start, struct mm_walk *walk); > struct mm_struct *mm; > struct vm_area_struct *vma; > void *private; > diff --git a/mm/pagewalk.c b/mm/pagewalk.c > index 1cbef99e9258..6bea79b95be3 100644 > --- a/mm/pagewalk.c > +++ b/mm/pagewalk.c > @@ -32,6 +32,14 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, > unsigned long next; > int err = 0; > > + if (walk->test_pmd) { > + err = walk->test_pmd(addr, end, pmd_offset(pud, 0UL), walk); > + if (err < 0) > + return err; > + if (err > 0) > + return 0; > + } Though this attempts to match semantics with test_walk() and be comprehensive just wondering what are the real world situations when page walking need to be aborted based on error condition at a given page table level.