From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x227cLWFktehhiuOKxsLMJdElLhRS5sZN4KJv+z2+NvAoljguLbeRH91+wzMUJ7A/56Kb2Frl ARC-Seal: i=1; a=rsa-sha256; t=1516908854; cv=none; d=google.com; s=arc-20160816; b=cenBIHuxC22OyuCJ35UhAaBrPL63AfaAD+ffBpRc0hHVm3/8Jv2sQUgWofpWcBhWwB WUZD9BdPEyFJDpFuoMEjMj9kIk6bWaSNMHDuDaFYEpos7lyv0Wz8L2y691GbjnRSCldB Ds5hwtopS7vedOKeqOUECTKgGBWtziYFe2UcXcb66in2wLMpqJTjUZ2StUuTHnGNggbh Ghumg2DKHD3dQkfaGK0GrWTqWMKcisEzXFmnWgYJzIpFXMbENuUZO5oNQ2B41KBT1e1T jRNcVtOr9n+kRwtUXA0Io08XrRoUCuhImMH1SvWaU9XAmAJW0yaH+2Ngbo4foBs9LI5+ Uu2g== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=content-transfer-encoding:content-language:in-reply-to:mime-version :user-agent:date:message-id:from:references:cc:to:subject :arc-authentication-results; bh=zccULjdLtg2TVHEbBDzU7TQYX7Cg6gZ3iSwNDA8G18k=; b=xDAd8e0DmP0yrscU6xQPP9XK3ThRbqxguoprTIJqHtfRdNy9hKgCMKCkvf42cJpPeQ PcUU6nO8hA39YAlxn6BbWvRmF3AREcTtQ0TcihIJSi/2KLUSVho5TYz835BUkbRRWfvg X4m+Gtj4aZbJYeLdkXNV/mSblAjHEzAIUVxscefW6dVkNLS5bkK10i9vKgaei4Eob+hE onhbWqOpADnJr9AnQorrGNoWuda605jzNSiFtoN19SL5NjTwQKhOr2cFybMD84pRBoPv Yoa8ufcD9UHUZElWjB16L+dAEBbFtdYzDYsMt89zhlftUGvZuFsTusYa669qqah74MWM QSUA== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: best guess record for domain of arjan@linux.intel.com designates 134.134.136.100 as permitted sender) smtp.mailfrom=arjan@linux.intel.com Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of arjan@linux.intel.com designates 134.134.136.100 as permitted sender) smtp.mailfrom=arjan@linux.intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.46,413,1511856000"; d="scan'208";a="29495322" Subject: Re: [RFC PATCH 1/2] x86/ibpb: Skip IBPB when we switch back to same user process To: Tim Chen , Peter Zijlstra , Andy Lutomirski Cc: LKML , KarimAllah Ahmed , Andi Kleen , Andrea Arcangeli , Ashok Raj , Asit Mallick , Borislav Petkov , Dan Williams , Dave Hansen , David Woodhouse , Greg Kroah-Hartman , "H . Peter Anvin" , Ingo Molnar , Janakarajan Natarajan , Joerg Roedel , Jun Nakajima , Laura Abbott , Linus Torvalds , Masami Hiramatsu , Paolo Bonzini , Radim Krcmar , Thomas Gleixner , Tom Lendacky , X86 ML References: <20180125085820.GV2228@hirez.programming.kicks-ass.net> <20180125092233.GE2295@hirez.programming.kicks-ass.net> <86541aca-8de7-163d-b620-083dddf29184@linux.intel.com> <20180125135055.GK2249@hirez.programming.kicks-ass.net> <20180125164139.GM2269@hirez.programming.kicks-ass.net> <20180125181852.GL2249@hirez.programming.kicks-ass.net> From: Arjan van de Ven Message-ID: <679180a8-cd7c-9200-224e-a93f0af77db7@linux.intel.com> Date: Thu, 25 Jan 2018 11:34:13 -0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1590523944221221739?= X-GMAIL-MSGID: =?utf-8?q?1590594219172257569?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: > > This patch tries to address the case when we do switch to init_mm and back. > Do you still have objections to the approach in this patch > to save the last active mm before switching to init_mm? how do you know the last active mm did not go away and started a new process with new content? (other than taking a reference which has other side effects)