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_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 8781FC433E3 for ; Fri, 17 Jul 2020 10:06:22 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4703520775 for ; Fri, 17 Jul 2020 10:06:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="kkj/1INF" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4703520775 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id B78CD6B0033; Fri, 17 Jul 2020 06:06:21 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B00C86B0037; Fri, 17 Jul 2020 06:06:21 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9C9B08D0032; Fri, 17 Jul 2020 06:06:21 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0233.hostedemail.com [216.40.44.233]) by kanga.kvack.org (Postfix) with ESMTP id 820B16B0033 for ; Fri, 17 Jul 2020 06:06:21 -0400 (EDT) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id ED84218352272 for ; Fri, 17 Jul 2020 10:06:20 +0000 (UTC) X-FDA: 77047137720.08.rest91_55030de26f0a Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin08.hostedemail.com (Postfix) with ESMTP id C2ADB180915B1 for ; Fri, 17 Jul 2020 10:06:20 +0000 (UTC) X-HE-Tag: rest91_55030de26f0a X-Filterd-Recvd-Size: 4869 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf39.hostedemail.com (Postfix) with ESMTP for ; Fri, 17 Jul 2020 10:06:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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; bh=K43ZCjJYMy6klub7Xq9DzX6bYQQEbWnMvoQ9/7nSlAU=; b=kkj/1INFxcsjPmAR7HcjcnkS3F gw7royqUQ/ZjChcF6ex998nRsQtVD8spWkTSkg3erjwYnMG/byuVK5dodJVY+nAW6ZP31fbitrYbx XASLEXixb7B5lLt+39tv+EAuZ75Q+jVs04bCADdjSmLIa6K1FEFih8/mS8J+WCt9OGM/80ogi0xe7 Xo8Q2rQXvnhMNB5RooczCx4UaqQye0duLIMEuN1+9eM+0/f9axdcXAkGf9PVove8rnp+8J6aJwjgJ 7IATAvjDIyeylA4nJvrm+w5utE1TjSJIxm2ynBiGTatJOtZYYD5WAttk8FyPDpfucP4CDH6R2FbwN 13hGovbQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jwNFs-0001WA-IX; Fri, 17 Jul 2020 10:06:13 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id CCBFF300446; Fri, 17 Jul 2020 12:06:10 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id B678029CF6F57; Fri, 17 Jul 2020 12:06:10 +0200 (CEST) Date: Fri, 17 Jul 2020 12:06:10 +0200 From: Peter Zijlstra To: ira.weiny@intel.com Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Andy Lutomirski , Dave Hansen , x86@kernel.org, Dan Williams , Vishal Verma , Andrew Morton , Fenghua Yu , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH RFC V2 17/17] x86/entry: Preserve PKRS MSR across exceptions Message-ID: <20200717100610.GH10769@hirez.programming.kicks-ass.net> References: <20200717072056.73134-1-ira.weiny@intel.com> <20200717072056.73134-18-ira.weiny@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200717072056.73134-18-ira.weiny@intel.com> X-Rspamd-Queue-Id: C2ADB180915B1 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 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 Fri, Jul 17, 2020 at 12:20:56AM -0700, ira.weiny@intel.com wrote: > First I'm not sure if adding this state to idtentry_state and having > that state copied is the right way to go. It seems like we should start > passing this by reference instead of value. But for now this works as > an RFC. Comments? As long as you keep sizeof(struct idtentry_state_t) <= sizeof(u64) or possibly 2*sizeof(unsigned long), code gen shouldn't be too horrid IIRC. You'll have to look at what the compiler makes of it. > Second, I'm not 100% happy with having to save the reference count in > the exception handler. It seems like a very ugly layering violation but > I don't see a way around it at the moment. So I've been struggling with that API, all the way from pks_update_protection() to that dev_access_{en,dis}able(). I _really_ hate it, but I see how you ended up with it. I wanted to propose something like: u32 current_pkey_save(int pkey, unsigned flags) { u32 *lpkr = get_cpu_ptr(&local_pkr); u32 pkr, saved = *lpkr; pkr = update_pkey_reg(saved, pkey, flags); if (pkr != saved) wrpkr(pkr); put_cpu_ptr(&local_pkr); return saved; } void current_pkey_restore(u32 pkr) { u32 *lpkr = get_cpu_ptr(&local_pkr); if (*lpkr != pkr) wrpkr(pkr); put_cpu_ptr(&local_pkr); } Together with: void pkey_switch(struct task_struct *prev, struct task_struct *next) { prev->pkr = this_cpu_read(local_pkr); if (prev->pkr != next->pkr) wrpkr(next->pkr); } But that's actually hard to frob into the kmap() model :-( The upside is that you only have 1 word of state, instead of the 2 you have now. > Third, this patch has gone through a couple of revisions as I've had > crashes which just don't make sense to me. One particular issue I've > had is taking a MCE during memcpy_mcsafe causing my WARN_ON() to fire. > The code path was a pmem copy and the ref count should have been > elevated due to dev_access_enable() but why was > idtentry_enter()->idt_save_pkrs() not called I don't know. Because MCEs are NMI-like and don't go through the normal interrupt path. MCEs are an abomination, please wear all the protective devices you can lay hands on when delving into that.