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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 902D3C742BD for ; Fri, 12 Jul 2019 13:51:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6428120863 for ; Fri, 12 Jul 2019 13:51:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727608AbfGLNvE (ORCPT ); Fri, 12 Jul 2019 09:51:04 -0400 Received: from mga07.intel.com ([134.134.136.100]:42897 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726907AbfGLNvE (ORCPT ); Fri, 12 Jul 2019 09:51:04 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Jul 2019 06:51:03 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.63,482,1557212400"; d="scan'208";a="166683426" Received: from smatond1-mobl1.amr.corp.intel.com (HELO [10.252.143.186]) ([10.252.143.186]) by fmsmga008.fm.intel.com with ESMTP; 12 Jul 2019 06:51:02 -0700 Subject: Re: [RFC v2 00/27] Kernel Address Space Isolation To: Alexandre Chartre , pbonzini@redhat.com, rkrcmar@redhat.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, kvm@vger.kernel.org, x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: konrad.wilk@oracle.com, jan.setjeeilers@oracle.com, liran.alon@oracle.com, jwadams@google.com, graf@amazon.de, rppt@linux.vnet.ibm.com References: <1562855138-19507-1-git-send-email-alexandre.chartre@oracle.com> <5cab2a0e-1034-8748-fcbe-a17cf4fa2cd4@intel.com> <2791712a-9f7b-18bc-e686-653181461428@oracle.com> From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <2791712a-9f7b-18bc-e686-653181461428@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 7/12/19 1:09 AM, Alexandre Chartre wrote: > On 7/12/19 12:38 AM, Dave Hansen wrote: >> I don't see the per-cpu areas in here.  But, the ASI macros in >> entry_64.S (and asi_start_abort()) use per-cpu data. > > We don't map all per-cpu areas, but only the per-cpu variables we need. ASI > code uses the per-cpu cpu_asi_session variable which is mapped when an ASI > is created (see patch 15/26): No fair! I had per-cpu variables just for PTI at some point and had to give them up! ;) > +    /* > +     * Map the percpu ASI sessions. This is used by interrupt handlers > +     * to figure out if we have entered isolation and switch back to > +     * the kernel address space. > +     */ > +    err = ASI_MAP_CPUVAR(asi, cpu_asi_session); > +    if (err) > +        return err; > > >> Also, this stuff seems to do naughty stuff (calling C code, touching >> per-cpu data) before the PTI CR3 writes have been done.  But, I don't >> see anything excluding PTI and this code from coexisting. > > My understanding is that PTI CR3 writes only happens when switching to/from > userland. While ASI enter/exit/abort happens while we are already in the > kernel, > so asi_start_abort() is not called when coming from userland and so not > interacting with PTI. OK, that makes sense. You only need to call C code when interrupted from something in the kernel (deeper than the entry code), and those were already running kernel C code anyway. If this continues to live in the entry code, I think you have a good clue where to start commenting. BTW, the PTI CR3 writes are not *strictly* about the interrupt coming from user vs. kernel. It's tricky because there's a window both in the entry and exit code where you are in the kernel but have a userspace CR3 value. You end up needing a CR3 write when you have a userspace CR3 value when the interrupt occurred, not only when you interrupt userspace itself.