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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 7F698C3A5A0 for ; Tue, 20 Aug 2019 01:41:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5F8F022CE8 for ; Tue, 20 Aug 2019 01:41:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729009AbfHTBls (ORCPT ); Mon, 19 Aug 2019 21:41:48 -0400 Received: from mga02.intel.com ([134.134.136.20]:57687 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728965AbfHTBlq (ORCPT ); Mon, 19 Aug 2019 21:41:46 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 19 Aug 2019 18:41:17 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,407,1559545200"; d="scan'208";a="262016113" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.41]) by orsmga001.jf.intel.com with ESMTP; 19 Aug 2019 18:41:17 -0700 Date: Mon, 19 Aug 2019 18:41:17 -0700 From: Sean Christopherson To: Andy Lutomirski Cc: Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , Thomas Gleixner , Ingo Molnar , Borislav Petkov , X86 ML , Jarkko Sakkinen , Joerg Roedel , "H. Peter Anvin" , kvm list , LKML , linux-sgx@vger.kernel.org Subject: Re: [RFC PATCH 08/21] KVM: x86: Add kvm_x86_ops hook to short circuit emulation Message-ID: <20190820014117.GJ1916@linux.intel.com> References: <20190727055214.9282-1-sean.j.christopherson@intel.com> <20190727055214.9282-9-sean.j.christopherson@intel.com> <20190730024940.GL21120@linux.intel.com> <25BBDA64-1253-4429-95AF-5D578684F6CC@amacapital.net> <20190819220150.GE1916@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 19, 2019 at 06:34:07PM -0700, Andy Lutomirski wrote: > On Mon, Aug 19, 2019 at 3:01 PM Sean Christopherson > wrote: > > > > On Thu, Aug 15, 2019 at 05:47:12PM -0700, Andy Lutomirski wrote: > > > > > > > > > >> On Jul 29, 2019, at 7:49 PM, Sean Christopherson wrote: > > > >> > > > >> On Sat, Jul 27, 2019 at 10:38:03AM -0700, Andy Lutomirski wrote: > > > >> On Fri, Jul 26, 2019 at 10:52 PM Sean Christopherson > > > >> wrote: > > > >>> > > > >>> Similar to the existing AMD #NPF case where emulation of the current > > > >>> instruction is not possible due to lack of information, virtualization > > > >>> of Intel SGX will introduce a scenario where emulation is not possible > > > >>> due to the VMExit occurring in an SGX enclave. And again similar to > > > >>> the AMD case, emulation can be initiated by kvm_mmu_page_fault(), i.e. > > > >>> outside of the control of the vendor-specific code. > > > >>> > > > >>> While the cause and architecturally visible behavior of the two cases > > > >>> is different, e.g. Intel SGX will inject a #UD whereas AMD #NPF is a > > > >>> clean resume or complete shutdown, the impact on the common emulation > > > >>> code is identical: KVM must stop emulation immediately and resume the > > > >>> guest. > > > >>> > > > >>> Replace the exisiting need_emulation_on_page_fault() with a more generic > > > >>> is_emulatable() kvm_x86_ops callback, which is called unconditionally > > > >>> by x86_emulate_instruction(). > > > >> > > > >> Having recently noticed that emulate_ud() is broken when the guest's > > > >> TF is set, I suppose I should ask: does your new code function > > > >> sensibly when TF is set? > > > > > > > > Barring a VMX fault injection interaction I'm not thinking of, yes. The > > > > SGX reaction to the #UD VM-Exit is to inject a #UD and resume the guest, > > > > pending breakpoints shouldn't be affected in any way (unless some other > > > > part of KVM mucks with them, e.g. when guest single-stepping is enabled). > > > > > > What I mean is: does the code actually do what you think it does if TF is > > > set? Right now, as I understand it, the KVM emulation code has a bug in > > > which some emulated faults also inject #DB despite the fact that the > > > instruction faulted, and the #DB seems to take precedence over the original > > > fault. This confuses the guest. > > > > Yes. The proposed change is to inject the #UD instead of calling into the > > emulator, and by inspection I've verified that all code that injects a #DB > > is either contained within the emulator or is mutually exclusive with an > > intercepted #UD. It's a qualified yes because I don't have an actual > > testcase to verify my literacy. I'll look into adding a test, either to > > the selftest/x86/sgx or to kvm-unit-tests. > > I wrote one, and it fails: > > # ./tools/testing/selftests/x86/syscall_arg_fault_32 > [RUN] SYSENTER with invalid state > [OK] Seems okay > [RUN] SYSCALL with invalid state > [SKIP] Illegal instruction > [RUN] SYSENTER with TF and invalid state > [OK] Seems okay > [RUN] SYSCALL with TF and invalid state > [WARN] Got stuck single-stepping -- you probably have a KVM bug > > emulate_ud() is buggy. Heh, yeah, I meant for the SGX case, e.g. SYSCALL from inside an enclave with RFLAGS.TF=1.