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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 746F1C3F2D1 for ; Tue, 3 Mar 2020 19:08:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 50CCB2073B for ; Tue, 3 Mar 2020 19:08:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730649AbgCCTI1 (ORCPT ); Tue, 3 Mar 2020 14:08:27 -0500 Received: from mga02.intel.com ([134.134.136.20]:36432 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727803AbgCCTI1 (ORCPT ); Tue, 3 Mar 2020 14:08:27 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 03 Mar 2020 11:08:26 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,511,1574150400"; d="scan'208";a="258479713" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by orsmga002.jf.intel.com with ESMTP; 03 Mar 2020 11:08:26 -0800 Date: Tue, 3 Mar 2020 11:08:26 -0800 From: Sean Christopherson To: Xiaoyao Li Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , hpa@zytor.com, Paolo Bonzini , Andy Lutomirski , tony.luck@intel.com, peterz@infradead.org, fenghua.yu@intel.com, x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 6/8] kvm: vmx: Extend VMX's #AC interceptor to handle split lock #AC happens in guest Message-ID: <20200303190826.GS1439@linux.intel.com> References: <20200206070412.17400-1-xiaoyao.li@intel.com> <20200206070412.17400-7-xiaoyao.li@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200206070412.17400-7-xiaoyao.li@intel.com> 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 Thu, Feb 06, 2020 at 03:04:10PM +0800, Xiaoyao Li wrote: > There are two types of #AC can be generated in Intel CPUs: > 1. legacy alignment check #AC; > 2. split lock #AC; > > Legacy alignment check #AC can be injected to guest if guest has enabled > alignemnet check. > > when host enables split lock detectin, i.e., split_lock_detect != off, > there will be an unexpected #AC in guest and intercepted by KVM because > KVM doesn't virtualize this feature to guest and hardware value of > MSR_TEST_CTRL.SLD bit stays unchanged when vcpu is running. > > To handle this unexpected #AC, treat guest just like host usermode that > calling handle_user_split_lock(): > - If host is sld_warn, it warns and set TIF_SLD so that __switch_to_xtra() > does the MSR_TEST_CTRL.SLD bit switching when control transfer to/from > this vcpu. > - If host is sld_fatal, forward #AC to userspace, the similar as sending > SIGBUS. > > Suggested-by: Sean Christopherson > Signed-off-by: Xiaoyao Li > --- > v3: > - Use handle_user_split_lock() to handle unexpected #AC in guest. > --- > arch/x86/kvm/vmx/vmx.c | 31 ++++++++++++++++++++++++++++--- > 1 file changed, 28 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index c475fa2aaae0..822211975e6c 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -4557,6 +4557,12 @@ static int handle_machine_check(struct kvm_vcpu *vcpu) > return 1; > } > > +static inline bool guest_cpu_alignment_check_enabled(struct kvm_vcpu *vcpu) > +{ > + return vmx_get_cpl(vcpu) == 3 && kvm_read_cr0_bits(vcpu, X86_CR0_AM) && > + (kvm_get_rflags(vcpu) & X86_EFLAGS_AC); > +} > + > static int handle_exception_nmi(struct kvm_vcpu *vcpu) > { > struct vcpu_vmx *vmx = to_vmx(vcpu); > @@ -4622,9 +4628,6 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu) > return handle_rmode_exception(vcpu, ex_no, error_code); > > switch (ex_no) { > - case AC_VECTOR: > - kvm_queue_exception_e(vcpu, AC_VECTOR, error_code); > - return 1; > case DB_VECTOR: > dr6 = vmcs_readl(EXIT_QUALIFICATION); > if (!(vcpu->guest_debug & > @@ -4653,6 +4656,28 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu) > kvm_run->debug.arch.pc = vmcs_readl(GUEST_CS_BASE) + rip; > kvm_run->debug.arch.exception = ex_no; > break; > + case AC_VECTOR: > + /* > + * Inject #AC back to guest only when guest enables legacy > + * alignment check. The comment should call out that checking split_lock_detect_enabled() is an optimization. /* * Reflect #AC to the guest if it's expecting the #AC, i.e. has * legacy alignment check enabled. Pre-check host split lock * support to avoid the VMREADs needed to check legacy #AC, * i.e. reflect the #AC if the only possible source is legacy * alignment checks. */ > + * Otherwise, it must be an unexpected split lock #AC of guest > + * since hardware SPLIT_LOCK_DETECT bit keeps unchanged set > + * when vcpu is running. In this case, treat guest the same as > + * user space application that calls handle_user_split_lock(): > + * - If sld_state = sld_warn, it sets TIF_SLD and disables SLD > + * for this vcpu thread. > + * - If sld_state = sld_fatal, we forward #AC to userspace, > + * similar as sending SIGBUS. I'd prefer to avoid talking about sld_state at all and instead keep those details in handle_user_split_lock(). > + */ > + if (!split_lock_detect_enabled() || > + guest_cpu_alignment_check_enabled(vcpu)) { > + kvm_queue_exception_e(vcpu, AC_VECTOR, error_code); > + return 1; > + } Something like: /* * Forward the #AC to userspace if kernel policy does not allow * temporarily disabling split lock detection. */ > + if (handle_user_split_lock(kvm_rip_read(vcpu))) > + return 1; > + /* fall through */ > default: > kvm_run->exit_reason = KVM_EXIT_EXCEPTION; > kvm_run->ex.exception = ex_no; > -- > 2.23.0 >