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 X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B31D8C4361B for ; Fri, 18 Dec 2020 21:59:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7CFFD23B54 for ; Fri, 18 Dec 2020 21:59:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726117AbgLRV7D (ORCPT ); Fri, 18 Dec 2020 16:59:03 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44318 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725813AbgLRV7C (ORCPT ); Fri, 18 Dec 2020 16:59:02 -0500 Received: from mail-ej1-x62a.google.com (mail-ej1-x62a.google.com [IPv6:2a00:1450:4864:20::62a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E925BC0617B0 for ; Fri, 18 Dec 2020 13:58:21 -0800 (PST) Received: by mail-ej1-x62a.google.com with SMTP id g20so5369389ejb.1 for ; Fri, 18 Dec 2020 13:58:21 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=awSkLxPxfKKMYWXrPvJO5HFC6rX6G+L4B8C1Llf9W6k=; b=hLBV/ED7BfeJwzOqpNCmMYChlwoFiY2KhYRYAh9YAvNmhTCp5Rl5vOtjXE5lcygy6P xGW8sekB6mt/nykunGGg68jfMt3kl8nI0XjHiLHAw/Jl44bdjco/2PBUvN8fBn5kDwON gE1GN8Dxfx9SDSEZCsA/rAzWdaPWuRJucgTnKWiNxbhGi9kV9JTK9FfS9yflDIleezEV bNojTL0m3+dL9+Bw8KoCwccFevhvpilw/9ImOHE0xnU4wNOK7nlI50q9eVjVevAIbBH7 jimQcsulIbzCWqGNVfNFRrbVZ+LrmM/3NVINZEg9b1lVwrhdpKkWdJLhFQIZGVrqeCxa DBdA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=awSkLxPxfKKMYWXrPvJO5HFC6rX6G+L4B8C1Llf9W6k=; b=e1DMDFtoLikkIauMkxMXZ4AtU7nqh2KdKDYOEy/oQ2/Ag8soW8BPwbtLMm9ov100ud RebMjw+/Mo9hjpYQnNGNPHp7qmRzmMME9wm9yHrH6Q1MlzFG6S89sUa2AblNNxuuWl8G Ndt/qoCBBYJyaDf7x68T6jWHOIEaS2BMSYGmKbSfCL2TdzBKvPnjVEIovqXSt5UFKT0M 6pNZXmSjI2Ktsiabysk6un6PzUaJ+XxPx7ta/QQEGEwLtc+BsBgReOyb4IzcM6Z/nOdU vwjlp5xoKWpqryvU2cR3CxPtHvsboxu18YStvxxchNW7DN2do78nZ2CTAPpN4LPP6fDu MAxg== X-Gm-Message-State: AOAM5317/tzN6nwG4avwzjcKAAg3+324jiz2HOCPUcBJUI4wneBzHmZM Thly4iOpXsfP+ON3yG18eiGeyuiDOHtjn54rslKJUA== X-Google-Smtp-Source: ABdhPJw+WBaQpu6K/EP/XCCpxET87+bULI/RU+iA1GSA2CpDe3vqce08alBcHTx2GShwo2pEUBLYdR2k0/3Rq4IDZN0= X-Received: by 2002:a17:906:edb2:: with SMTP id sa18mr5756613ejb.264.1608328700420; Fri, 18 Dec 2020 13:58:20 -0800 (PST) MIME-Version: 1.0 References: <20201106232908.364581-1-ira.weiny@intel.com> <20201106232908.364581-5-ira.weiny@intel.com> <871rfoscz4.fsf@nanos.tec.linutronix.de> <87mtycqcjf.fsf@nanos.tec.linutronix.de> <878s9vqkrk.fsf@nanos.tec.linutronix.de> <875z4yrfhr.fsf@nanos.tec.linutronix.de> In-Reply-To: <875z4yrfhr.fsf@nanos.tec.linutronix.de> From: Dan Williams Date: Fri, 18 Dec 2020 13:58:09 -0800 Message-ID: Subject: Re: [PATCH V3 04/10] x86/pks: Preserve the PKRS MSR on context switch To: Thomas Gleixner Cc: "Weiny, Ira" , Ingo Molnar , Borislav Petkov , Andy Lutomirski , Peter Zijlstra , Dave Hansen , Fenghua Yu , X86 ML , Linux Kernel Mailing List , Andrew Morton , Linux Doc Mailing List , linux-nvdimm , Linux MM , linux-kselftest@vger.kernel.org, Greg KH Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 18, 2020 at 1:06 PM Thomas Gleixner wrote: > > On Fri, Dec 18 2020 at 11:20, Dan Williams wrote: > > On Fri, Dec 18, 2020 at 5:58 AM Thomas Gleixner wrote: > > [..] > >> 5) The DAX case which you made "work" with dev_access_enable() and > >> dev_access_disable(), i.e. with yet another lazy approach of > >> avoiding to change a handful of usage sites. > >> > >> The use cases are strictly context local which means the global > >> magic is not used at all. Why does it exist in the first place? > >> > >> Aside of that this global thing would never work at all because the > >> refcounting is per thread and not global. > >> > >> So that DAX use case is just a matter of: > >> > >> grant/revoke_access(DEV_PKS_KEY, READ/WRITE) > >> > >> which is effective for the current execution context and really > >> wants to be a distinct READ/WRITE protection and not the magic > >> global thing which just has on/off. All usage sites know whether > >> they want to read or write. > > > > I was tracking and nodding until this point. Yes, kill the global / > > kmap() support, but if grant/revoke_access is not integrated behind > > kmap_{local,atomic}() then it's not a "handful" of sites that need to > > be instrumented it's 100s. Are you suggesting that "relaxed" mode > > enforcement is a way to distribute the work of teaching driver writers > > that they need to incorporate explicit grant/revoke-read/write in > > addition to kmap? The entire reason PTE_DEVMAP exists was to allow > > get_user_pages() for PMEM and not require every downstream-GUP code > > path to specifically consider whether it was talking to PMEM or RAM > > pages, and certainly not whether they were reading or writing to it. > > kmap_local() is fine. That can work automatically because it's strict > local to the context which does the mapping. > > kmap() is dubious because it's a 'global' mapping as dictated per > HIGHMEM. So doing the RELAXED mode for kmap() is sensible I think to > identify cases where the mapped address is really handed to a different > execution context. We want to see those cases and analyse whether this > can't be solved in a different way. That's why I suggested to do a > warning in that case. > > Also vs. the DAX use case I really meant the code in fs/dax and > drivers/dax/ itself which is handling this via dax_read_[un]lock. > > Does that make more sense? Yup, got it. The dax code can be precise wrt to PKS in a way that kmap_local() cannot.