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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A1E09C25B50 for ; Sat, 21 Jan 2023 00:29:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230042AbjAUA3x (ORCPT ); Fri, 20 Jan 2023 19:29:53 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41172 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229693AbjAUA3t (ORCPT ); Fri, 20 Jan 2023 19:29:49 -0500 Received: from mail-pf1-x431.google.com (mail-pf1-x431.google.com [IPv6:2607:f8b0:4864:20::431]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A8FFD458A3 for ; Fri, 20 Jan 2023 16:29:12 -0800 (PST) Received: by mail-pf1-x431.google.com with SMTP id 20so5157181pfu.13 for ; Fri, 20 Jan 2023 16:29:12 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=EbY+DpmZALU1xtabL7k2YgspkrWnr2TPU7+U6NxTXL0=; b=SLCQrWTEWqx3z5HCeCKrXUYH9kq0GSQ2Tz6DveA2dfjxzEDJFQFEYKh0gQ3MERWsQA 0VmdDTj5e/w3RGYj3x0I3NyympDFqZkTPr5CuZLM8w7vX605wQrcs8EXbrA9Hd0vtPlp iZgTnxx5283Zrc7uo0X5pcU85zNidYfKSoI8U+MxpS84xQYeg3BFpY502zhWbO7YOqYw tbGfYZZ/ihZ9RLlWe22al9abwSIOGSueZJkwmT25rNpCLT386NAYIKo6/rm2dM/ACy72 hoYvIqO7bpuU4LDneG4qARBbBLsN2cQIV2T7Lbvc5V4+o0SzZe3GZTDyrjpdE9+u009a xMKw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=EbY+DpmZALU1xtabL7k2YgspkrWnr2TPU7+U6NxTXL0=; b=lpAI/YH6ACgBMg6zcO9+eueWHv65NKBFlr/gwLtdxYiQgw+v8kul2Y7qj3TPYHulNg 0qqmsu0Ac0yBA8aUth8MJaW+H6KbK3OWDkY4sEldwEFqhFNufQX66FPSEjcebppN/zAW Zy+JZKT8JmhGefxonxKoZYJ+fEV9SSYqsRMajzrm41FAuMM3qs+cXzEThWzLzKCfQHxO UAfcev9yBX8IHC0+/o0WF/wvpG/1MeP2SO1M8LdwaFqQ7bytQ+RMBh6LpvZsBKvmVIhE JZCXagXZKV+/rD9RFVmMku+HOQBk11CmEP9PBMNpZk0d4SGqt3uPXNKQdV23xrmB1jJQ 6kLQ== X-Gm-Message-State: AFqh2kofiF5dhkCcYfAWLkDKz/itGRTRjKELdfaslTjEvj/lVViX6+2N jPVftTFCSlCXm2ZcXmqpGxlZ1Q== X-Google-Smtp-Source: AMrXdXu8EN+twWwhPAqOi03K0719ef3ZgbBTz9G+K40Gu8sQutLDARHdWCAFCSeWIB/2Nx6CHn21NA== X-Received: by 2002:a62:d448:0:b0:58b:cb1b:978f with SMTP id u8-20020a62d448000000b0058bcb1b978fmr28890pfl.1.1674260882188; Fri, 20 Jan 2023 16:28:02 -0800 (PST) Received: from google.com (7.104.168.34.bc.googleusercontent.com. [34.168.104.7]) by smtp.gmail.com with ESMTPSA id a1-20020aa795a1000000b0058119caa82csm13924239pfk.205.2023.01.20.16.28.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Jan 2023 16:28:01 -0800 (PST) Date: Sat, 21 Jan 2023 00:27:58 +0000 From: Sean Christopherson To: Ackerley Tng Cc: linux-kselftest@vger.kernel.org, pbonzini@redhat.com, isaku.yamahata@intel.com, sagis@google.com, erdemaktas@google.com, afranji@google.com, runanwang@google.com, shuah@kernel.org, drjones@redhat.com, maz@kernel.org, bgardon@google.com, jmattson@google.com, dmatlack@google.com, peterx@redhat.com, oupton@google.com, ricarkol@google.com, yang.zhong@intel.com, wei.w.wang@intel.com, xiaoyao.li@intel.com, pgonda@google.com, marcorr@google.com, eesposit@redhat.com, borntraeger@de.ibm.com, eric.auger@redhat.com, wangyanan55@huawei.com, aaronlewis@google.com, vkuznets@redhat.com, pshier@google.com, axelrasmussen@google.com, zhenzhong.duan@intel.com, maciej.szmigiero@oracle.com, like.xu@linux.intel.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [RFC PATCH v3 08/31] KVM: selftests: Require GCC to realign stacks on function entry Message-ID: References: <20230121001542.2472357-1-ackerleytng@google.com> <20230121001542.2472357-9-ackerleytng@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230121001542.2472357-9-ackerleytng@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 21, 2023, Ackerley Tng wrote: > Some SSE instructions assume a 16-byte aligned stack, and GCC compiles > assuming the stack is aligned: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=40838. This combination > results in a #GP in guests. > > Adding this compiler flag will generate an alternate prologue and > epilogue to realign the runtime stack, which makes selftest code > slower and bigger, but this is okay since we do not need selftest code > to be extremely performant. Huh, I had completely forgotten that this is why SSE is problematic. I ran into this with the base UPM selftests and just disabled SSE. /facepalm. We should figure out exactly what is causing a misaligned stack. As you've noted, the x86-64 ABI requires a 16-byte aligned RSP. Unless I'm misreading vm_arch_vcpu_add(), the starting stack should be page aligned, which means something is causing the stack to become unaligned at runtime. I'd rather hunt down that something than paper over it by having the compiler force realignment. > Similar issue discussed at > https://lore.kernel.org/all/CAGtprH9yKvuaF5yruh3BupQe4BxDGiBQk3ExtY2m39yP-tppsg@mail.gmail.com/ > > Signed-off-by: Ackerley Tng > --- > tools/testing/selftests/kvm/Makefile | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile > index 317927d9c55bd..5f9cc1e6ee67e 100644 > --- a/tools/testing/selftests/kvm/Makefile > +++ b/tools/testing/selftests/kvm/Makefile > @@ -205,7 +205,7 @@ LINUX_TOOL_ARCH_INCLUDE = $(top_srcdir)/tools/arch/x86/include > else > LINUX_TOOL_ARCH_INCLUDE = $(top_srcdir)/tools/arch/$(ARCH)/include > endif > -CFLAGS += -Wall -Wstrict-prototypes -Wuninitialized -O2 -g -std=gnu99 \ > +CFLAGS += -mstackrealign -Wall -Wstrict-prototypes -Wuninitialized -O2 -g -std=gnu99 \ > -fno-stack-protector -fno-PIE -I$(LINUX_TOOL_INCLUDE) \ > -I$(LINUX_TOOL_ARCH_INCLUDE) -I$(LINUX_HDR_PATH) -Iinclude \ > -I$( -- > 2.39.0.246.g2a6d74b583-goog >