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[217.140.110.172]) by mx.google.com with ESMTP id 11si13501527ejy.102.2019.07.28.07.19.29 for ; Sun, 28 Jul 2019 07:19:30 -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 3517E344; Sun, 28 Jul 2019 07:19:29 -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 698B53F575; Sun, 28 Jul 2019 07:19:22 -0700 (PDT) Subject: Re: [PATCH v9 12/21] mm: pagewalk: Allow walking without vma 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> <20190722154210.42799-13-steven.price@arm.com> From: Anshuman Khandual Message-ID: <7fc50563-7d5d-7270-5a6a-63769e9c335a@arm.com> Date: Sun, 28 Jul 2019 19:50:02 +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: <20190722154210.42799-13-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: > Since 48684a65b4e3: "mm: pagewalk: fix misbehavior of walk_page_range > for vma(VM_PFNMAP)", page_table_walk() will report any kernel area as > a hole, because it lacks a vma. > > This means each arch has re-implemented page table walking when needed, > for example in the per-arch ptdump walker. > > Remove the requirement to have a vma except when trying to split huge > pages. > > Signed-off-by: Steven Price > --- > mm/pagewalk.c | 25 +++++++++++++++++-------- > 1 file changed, 17 insertions(+), 8 deletions(-) > > diff --git a/mm/pagewalk.c b/mm/pagewalk.c > index 98373a9f88b8..1cbef99e9258 100644 > --- a/mm/pagewalk.c > +++ b/mm/pagewalk.c > @@ -36,7 +36,7 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, > do { > again: > next = pmd_addr_end(addr, end); > - if (pmd_none(*pmd) || !walk->vma) { > + if (pmd_none(*pmd)) { > if (walk->pte_hole) > err = walk->pte_hole(addr, next, walk); > if (err) > @@ -59,9 +59,14 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end, > if (!walk->pte_entry) > continue; > > - split_huge_pmd(walk->vma, pmd, addr); > - if (pmd_trans_unstable(pmd)) > - goto again; > + if (walk->vma) { > + split_huge_pmd(walk->vma, pmd, addr); Check for a PMD THP entry before attempting to split it ? > + if (pmd_trans_unstable(pmd)) > + goto again; > + } else if (pmd_leaf(*pmd)) { > + continue; > + } > + > err = walk_pte_range(pmd, addr, next, walk); > if (err) > break; > @@ -81,7 +86,7 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, > do { > again: > next = pud_addr_end(addr, end); > - if (pud_none(*pud) || !walk->vma) { > + if (pud_none(*pud)) { > if (walk->pte_hole) > err = walk->pte_hole(addr, next, walk); > if (err) > @@ -95,9 +100,13 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end, > break; > } > > - split_huge_pud(walk->vma, pud, addr); > - if (pud_none(*pud)) > - goto again; > + if (walk->vma) { > + split_huge_pud(walk->vma, pud, addr); Check for a PUD THP entry before attempting to split it ? > + if (pud_none(*pud)) > + goto again; > + } else if (pud_leaf(*pud)) { > + continue; > + } This is bit cryptic. walk->vma check should be inside a helper is_user_page_table() or similar to make things clear. p4d_leaf() check missing in walk_p4d_range() for kernel page table walk ? Wondering if p?d_leaf() test should be moved earlier while calling p?d_entry() for kernel page table walk.