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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 45FEEC433EF for ; Thu, 12 May 2022 15:16:15 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A63A36B0074; Thu, 12 May 2022 11:16:14 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A13F06B0075; Thu, 12 May 2022 11:16:14 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 88C676B0078; Thu, 12 May 2022 11:16:14 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 76E2F6B0074 for ; Thu, 12 May 2022 11:16:14 -0400 (EDT) Received: from smtpin02.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay13.hostedemail.com (Postfix) with ESMTP id 4792E60507 for ; Thu, 12 May 2022 15:16:14 +0000 (UTC) X-FDA: 79457441868.02.06CD583 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by imf11.hostedemail.com (Postfix) with ESMTP id 8748340058 for ; Thu, 12 May 2022 15:16:08 +0000 (UTC) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1652368572; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=grsC0w+E9Jfgx2nf3sde57yzh3ij8Mi1ObW9I0pQcXg=; b=QP9d2vJHTocBeVJGSXckP+GiDE7SnKW6S8OcPZe9+uq845NpdBDnLqssIS2OsTgDSmHBxu AM9gkU2DIL5w5tw42R/cVp6oWGGpHN7Y3//rkCDvlhoII9OBk25WB2mjb6hgVJhKFEavMv estScOX8SotUNTYuZs2TsWMf6TMSblYYqjWkLQhxN0Wk2FL1qsrqNp8xz3bFrS/WjlwMc0 USLLNJTNsNGxf9qcoD930NiRt/dohlPDR462wfK+abm/5ZLP6Ft/dLWIbRG3TS0fgGCtJc OYFtUFXKa+AOGS/3I7sLz8OjK2M4wb8iYnGqMT5nIo+8JiMOk+aI0riolxJyHA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1652368572; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=grsC0w+E9Jfgx2nf3sde57yzh3ij8Mi1ObW9I0pQcXg=; b=iuRZSkwtyMK+lJI9aS6Ba4q73+eZ+FZGunSKYXQB3nHdm4GEmHTNOE/mVJ/PcUpfsVKJac V4fUVoxCgKjP7GAg== To: Peter Zijlstra Cc: "Kirill A. Shutemov" , Dave Hansen , Andy Lutomirski , x86@kernel.org, Andrey Ryabinin , Alexander Potapenko , Dmitry Vyukov , "H . J . Lu" , Andi Kleen , Rick Edgecombe , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFCv2 05/10] x86/mm: Provide untagged_addr() helper In-Reply-To: References: <20220511022751.65540-1-kirill.shutemov@linux.intel.com> <20220511022751.65540-7-kirill.shutemov@linux.intel.com> <87a6bmx5lt.ffs@tglx> Date: Thu, 12 May 2022 17:16:11 +0200 Message-ID: <87sfpevl1g.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain X-Rspamd-Queue-Id: 8748340058 X-Stat-Signature: ot851hkhe3ppwi4r9u789194p9zbo5fy Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=linutronix.de header.s=2020 header.b=QP9d2vJH; dkim=pass header.d=linutronix.de header.s=2020e header.b=iuRZSkwt; dmarc=pass (policy=none) header.from=linutronix.de; spf=pass (imf11.hostedemail.com: domain of tglx@linutronix.de designates 193.142.43.55 as permitted sender) smtp.mailfrom=tglx@linutronix.de X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1652368568-677469 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, May 12 2022 at 16:23, Peter Zijlstra wrote: > On Thu, May 12, 2022 at 03:06:38PM +0200, Thomas Gleixner wrote: > >> #define untagged_addr(addr) ({ \ >> u64 __addr = (__force u64)(addr); \ >> \ >> __addr &= current->thread.lam_untag_mask; \ >> (__force __typeof__(addr))__addr; \ >> }) >> >> No conditionals, fast _and_ correct. Setting this untag mask up once >> when LAM is enabled is not rocket science. > > But that goes wrong if someone ever wants to untag a kernel address and > not use the result for access_ok(). > > I'd feel better about something like: > > s64 __addr = (addr); > s64 __sign = __addr; > > __sign >>= 63; > __sign &= lam_untag_mask; that needs to be __sign &= ~lam_untag_mask; > __addr &= lam_untag_mask; > __addr |= __sign; > > __addr; > > Which simply extends bit 63 downwards -- although possibly there's an > easier way to do that, this is pretty gross. For the price of a conditional: __addr &= lam_untag_mask; if (__addr & BIT(63)) __addr |= ~lam_untag_mask; Now you have the choice between gross and ugly. Thanks, tglx