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[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-kselftest@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 >