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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id d6si17034277pgk.129.2019.05.01.18.44.25 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 01 May 2019 18:44:25 -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=VYE7PKot; 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=y53VfYOiA/MXZf8Wo2SPne1jzkwcek0/8OpLxdvECJY=; b=VYE7PKotQxs/oJ2smNzmRlGn7 vC6rHSwDHr9gQfV0YtYSV2yUVg4ZPWpN9SNVskAe1K9CRoRofZ7esUPRUzjgohFzwqaecc+2w3qJz hrXp6+62HOmTD1Im9ww2zQqLMPNvskirWueS2ha/Fs1kBPGsLEI2dMoz8IxeSDP3bDjgtlU7qzDFG s77flvY9VkhFc1AItHA6SNFCp1m8POxF8PBmqMR/XjZt2UrOQpxJcfqvVJpx3IRy6MqZR3t11mD0N kdnTGVwr45z2IZj31/ujIKsogxqwCXe+cepwam885j4sa5uFaQ4AEudexWUQk5FxE2t0N04oTFd4T 32ML/tHlQ==; Received: from willy by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1hM0lq-0002IA-F3; Thu, 02 May 2019 01:44:22 +0000 Date: Wed, 1 May 2019 18:44:22 -0700 From: Matthew Wilcox To: Jann Horn Cc: Jan Kara , Linux-MM Subject: Re: get_user_pages pinning: 2^22 page refs max? Message-ID: <20190502014422.GA8099@bombadil.infradead.org> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.2 (2017-12-15) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000800, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, May 01, 2019 at 06:19:00PM -0400, Jann Horn wrote: > Regarding the LSFMM talk today: > So with the page ref bias, the maximum number of page references will > be something like 2^22, right? Is the bias only applied to writable > references or also readonly ones? 2^21, because it's going to get caught by the < 0 check. I think that's fine, though. Anyone trying to map that page so many times is clearly doing something either malicious or inadvertently very wrong. After the 2 millionth time, attempting to pin the page will fail, and the application will have to deal with that failure.