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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 94D5DC35247 for ; Mon, 3 Feb 2020 20:54:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6EC9921D7D for ; Mon, 3 Feb 2020 20:54:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727044AbgBCUy1 (ORCPT ); Mon, 3 Feb 2020 15:54:27 -0500 Received: from mga02.intel.com ([134.134.136.20]:59195 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725372AbgBCUy0 (ORCPT ); Mon, 3 Feb 2020 15:54:26 -0500 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 03 Feb 2020 12:54:26 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,398,1574150400"; d="scan'208";a="403572253" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by orsmga005.jf.intel.com with ESMTP; 03 Feb 2020 12:54:26 -0800 Date: Mon, 3 Feb 2020 12:54:26 -0800 From: Sean Christopherson To: Xiaoyao Li Cc: Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Andy Lutomirski , x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, David Laight Subject: Re: [PATCH v2 3/6] kvm: x86: Emulate split-lock access as a write Message-ID: <20200203205426.GF19638@linux.intel.com> References: <20200203151608.28053-1-xiaoyao.li@intel.com> <20200203151608.28053-4-xiaoyao.li@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200203151608.28053-4-xiaoyao.li@intel.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Feb 03, 2020 at 11:16:05PM +0800, Xiaoyao Li wrote: > If split lock detect is enabled (warn/fatal), #AC handler calls die() > when split lock happens in kernel. > > A sane guest should never tigger emulation on a split-lock access, but > it cannot prevent malicous guest from doing this. So just emulating the > access as a write if it's a split-lock access to avoid malicous guest > polluting the kernel log. > > More detail analysis can be found: > https://lkml.kernel.org/r/20200131200134.GD18946@linux.intel.com > > Signed-off-by: Xiaoyao Li > --- > arch/x86/kvm/x86.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 2d3be7f3ad67..821b7404c0fd 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -5847,6 +5847,13 @@ static int emulator_write_emulated(struct x86_emulate_ctxt *ctxt, > (cmpxchg64((u64 *)(ptr), *(u64 *)(old), *(u64 *)(new)) == *(u64 *)(old)) > #endif > > +static inline bool across_cache_line_access(gpa_t gpa, unsigned int bytes) s/across/split so as not to introduce another name. > +{ > + unsigned int cache_line_size = cache_line_size(); > + > + return (gpa & (cache_line_size - 1)) + bytes > cache_line_size; I'd prefer to use the same logic as the page-split to avoid having to reason about the correctness of two different algorithms. > +} > + > static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt, > unsigned long addr, > const void *old, > @@ -5873,6 +5880,10 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt, > if (((gpa + bytes - 1) & PAGE_MASK) != (gpa & PAGE_MASK)) > goto emul_write; > > + if (get_split_lock_detect_state() != sld_off && > + across_cache_line_access(gpa, bytes)) > + goto emul_write; As an alternative to the above, the page/line splits can be handled in a single check, e.g. page_line_mask = PAGE_MASK; if (is_split_lock_detect_enabled()) page_line_mask = cache_line_size() - 1; if (((gpa + bytes - 1) & page_line_mask) != (gpa & page_line_mask)) goto emul_write; > + > if (kvm_vcpu_map(vcpu, gpa_to_gfn(gpa), &map)) > goto emul_write; > > -- > 2.23.0 >