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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id l4si17297908pjq.69.2019.07.25.14.42.34 for (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Thu, 25 Jul 2019 14:42:34 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) client-ip=2607:7c80:54:e::133; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b="e/Yzp6j8"; spf=pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=willy@infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=JNOo0Dhi9UDinqug0uYA1LHheZfDibP+WEcEG6xvIBA=; b=e/Yzp6j8Alk5/730XXwU0FDWq rr3okQdzLCE/J4OLyeEPbCRO5XaSEEqvUQNRuRdDTG/W3OlD1FAjSaxvbulJP4bbEv2K/AQ2pdD7U C25B6yg420c7m5I/Iv0H7H3aTu60UCDWNz1VIrgdDL7SjaSToKp3xhjFnK0FAT+OdGd8tjn7T0BiL FVnp2v5FBeoStt238IAx1keeH1uoGWywMyOzwIoA2i0vmW6dd0U6Kfa62LYSOi7Vnd4DWO1YOgjNg 0PLrZ06JDUhTYMwDhiWauSPYZcheWxkHZREuSCfc07MneufWREPlpo1Hg9S9UoGbIioPLs5HnL1tq WlAQZfXjQ==; Received: from willy by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1hqlVG-0004iU-Tb; Thu, 25 Jul 2019 21:42:22 +0000 Date: Thu, 25 Jul 2019 14:42:22 -0700 From: Matthew Wilcox To: Russell King - ARM Linux admin Cc: Anshuman Khandual , Mark Rutland , Kees Cook , Sri Krishna chowdary , Ard Biesheuvel , Masahiro Yamada , Tetsuo Handa , x86@kernel.org, Dave Hansen , linux-kernel@vger.kernel.org, Steven Price , linux-mm@kvack.org, Mark Brown , Andrew Morton , Michal Hocko , linux-arm-kernel@lists.infradead.org Subject: Re: [RFC] mm/pgtable/debug: Add test validating architecture page table helpers Message-ID: <20190725214222.GG30641@bombadil.infradead.org> References: <1564037723-26676-1-git-send-email-anshuman.khandual@arm.com> <1564037723-26676-2-git-send-email-anshuman.khandual@arm.com> <20190725143920.GW363@bombadil.infradead.org> <20190725213858.GK1330@shell.armlinux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190725213858.GK1330@shell.armlinux.org.uk> User-Agent: Mutt/1.11.4 (2019-03-13) 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 Thu, Jul 25, 2019 at 10:38:58PM +0100, Russell King - ARM Linux admin wrote: > On Thu, Jul 25, 2019 at 07:39:21AM -0700, Matthew Wilcox wrote: > > But 'page' isn't necessarily PMD-aligned. I don't think we can rely on > > architectures doing the right thing if asked to make a PMD for a randomly > > aligned page. > > > > How about finding the physical address of something like kernel_init(), > > and using the corresponding pte/pmd/pud/p4d/pgd that encompasses that > > address? It's also better to pass in the pfn/page rather than using global > > variables to communicate to the test functions. > > There are architectures (32-bit ARM) where the kernel is mapped using > section mappings, and we don't expect the Linux page table walking to > work for section mappings. This test doesn't go so far as to insert the PTE/PMD/PUD/... into the page tables. It merely needs an appropriately aligned PFN to create a PTE/PMD/PUD/... from.