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=-4.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 13B26C433E3 for ; Thu, 23 Jul 2020 19:53:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E5B1B2086A for ; Thu, 23 Jul 2020 19:53:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="uFXjXbf4"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="IP9QMcXa" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726503AbgGWTxY (ORCPT ); Thu, 23 Jul 2020 15:53:24 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:60814 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725894AbgGWTxY (ORCPT ); Thu, 23 Jul 2020 15:53:24 -0400 From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1595534000; 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=X0c32+NIatB9JM6CXey+0z41GiQlbz97j0f7TqXtlAY=; b=uFXjXbf4Yp8aNwTNbxJjHuHwYks2TWbYKgxnG7Jr1JWxhF+duZctOadDtngKL2Pntdlcr5 AvKP6qpAvouuuiV9yCUIMDIlbTkuWxZoD7TQabGmbTA0mjtTK30eJeHRVEjwqxpk03fPUS tTHuvjt5xvqU5prBd0+EqsNeg67IAnB6WbSAufCh1h3bnSTSGxuR6+oxKhzw+WygKCqZiO DzSskQq90BXIC5ugNwOtkIPpZNUuGtTQ2f/N1n2GVcGCN+TQeOR0jfxYFV4o6wzageqeaB yb7Im752qEUzAhYy4YEc/rgs/zaCt1/1hFkXqJTndrZAWzomDhEhunfLRUOtbQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1595534000; 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=X0c32+NIatB9JM6CXey+0z41GiQlbz97j0f7TqXtlAY=; b=IP9QMcXa1ApuQm3+KZmrUmtJj6z7QxJxyk9fPf+kLhbrZgzz7HlWKdlTZhcyEP2iMZoUqw PGdJS5nkBsmndqAQ== To: ira.weiny@intel.com, Ingo Molnar , Borislav Petkov , Andy Lutomirski , Peter Zijlstra Cc: Ira Weiny , 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 In-Reply-To: <20200717072056.73134-18-ira.weiny@intel.com> References: <20200717072056.73134-1-ira.weiny@intel.com> <20200717072056.73134-18-ira.weiny@intel.com> Date: Thu, 23 Jul 2020 21:53:20 +0200 Message-ID: <87r1t2vwi7.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org Ira, ira.weiny@intel.com writes: > ... > // ref == 0 > dev_access_enable() // ref += 1 ==> disable protection > irq() > // enable protection > // ref = 0 > _handler() > dev_access_enable() // ref += 1 ==> disable protection > dev_access_disable() // ref -= 1 ==> enable protection > // WARN_ON(ref != 0) > // disable protection > do_pmem_thing() // all good here > dev_access_disable() // ref -= 1 ==> 0 ==> enable protection ... > First I'm not sure if adding this state to idtentry_state and having > that state copied is the right way to go. Adding the state to idtentry_state is fine at least for most interrupts and exceptions. Emphasis on most. #PF does not work because #PF can schedule. > It seems like we should start passing this by reference instead of > value. But for now this works as an RFC. Comments? Works as in compiles, right? static void noinstr idt_save_pkrs(idtentry_state_t state) { state.foo = 1; } How is that supposed to change the caller state? C programming basics. > 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. That state is strict per task, right? So why do you want to store it anywhere else that in task/thread storage. That solves your problem of #PF scheduling nicely. > 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 #MC does not go through idtentry_enter(). Neither do #NMI, #DB, #BP. > Finally, it looks like the entry/exit code is being refactored into > common code. So likely this is best handled somewhat there. Because > this can be predicated on CONFIG_ARCH_HAS_SUPERVISOR_PKEYS and handled > in a generic fashion. But that is a ways off I think. The invocation of save/restore might be placed in generic code at least for the common exception and interrupt entries. > +static void noinstr idt_save_pkrs(idtentry_state_t state) *state. See above. > +#else > +/* Define as macros to prevent conflict of inline and noinstr */ > +#define idt_save_pkrs(state) > +#define idt_restore_pkrs(state) Empty inlines do not need noinstr because they are optimized out. If you want inlines in a noinstr section then use __always_inline > /** > * idtentry_enter - Handle state tracking on ordinary idtentries > * @regs: Pointer to pt_regs of interrupted context > @@ -604,6 +671,8 @@ idtentry_state_t noinstr idtentry_enter(struct pt_regs *regs) > return ret; > } > > + idt_save_pkrs(ret); No. This really has no business to be called before the state is established. It's not something horribly urgent and write_pkrs() is NOT noinstr and invokes wrmsrl() which is subject to tracing. > + > + idt_restore_pkrs(state); This one is placed correctly. Thanks, tglx