* Re: [stable:linux-5.15.y 5373/9027] arch/x86/kvm/hyperv.c:2185:5: warning: stack frame size (1036) exceeds limit (1024) in 'kvm_hv_hypercall' [not found] <202208142025.NHKErAjq-lkp@intel.com> @ 2022-08-15 8:10 ` Vitaly Kuznetsov 2022-08-15 17:05 ` Nathan Chancellor 0 siblings, 1 reply; 2+ messages in thread From: Vitaly Kuznetsov @ 2022-08-15 8:10 UTC (permalink / raw) To: kernel test robot, kvm Cc: llvm, kbuild-all, linux-kernel, Greg Kroah-Hartman, Paolo Bonzini kernel test robot <lkp@intel.com> writes: > Hi Vitaly, > > FYI, the error/warning still remains. > Yes, this is expected as the patch which is supposed to 'fix' this is still pendind. The latest version is here: https://lore.kernel.org/kvm/20220803134540.399220-1-vkuznets@redhat.com/ ... > tree: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git linux-5.15.y > head: 7217df81279835a7aee62a07aabb7b8fb8c766f2 > commit: cb188e07105f2216f5efbefac95df4b6ce266906 [5373/9027] KVM: x86: hyper-v: HVCALL_SEND_IPI_EX is an XMM fast hypercall > config: i386-allmodconfig (https://download.01.org/0day-ci/archive/20220814/202208142025.NHKErAjq-lkp@intel.com/config) > compiler: clang version 16.0.0 (https://github.com/llvm/llvm-project 52cd00cabf479aa7eb6dbb063b7ba41ea57bce9e) > reproduce (this is a W=1 build): > wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross > chmod +x ~/bin/make.cross > # https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?id=cb188e07105f2216f5efbefac95df4b6ce266906 > git remote add stable https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git > git fetch --no-tags stable linux-5.15.y > git checkout cb188e07105f2216f5efbefac95df4b6ce266906 > # save the config file > mkdir build_dir && cp config build_dir/.config > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 SHELL=/bin/bash arch/x86/kvm/ > > If you fix the issue, kindly add following tag where applicable > Reported-by: kernel test robot <lkp@intel.com> > > All warnings (new ones prefixed by >>): > >>> arch/x86/kvm/hyperv.c:2185:5: warning: stack frame size (1036) exceeds limit (1024) in 'kvm_hv_hypercall' [-Wframe-larger-than] > int kvm_hv_hypercall(struct kvm_vcpu *vcpu) > ^ > 1 warning generated. > > > vim +/kvm_hv_hypercall +2185 arch/x86/kvm/hyperv.c > > 4ad81a91119df7 Vitaly Kuznetsov 2021-05-21 2184 > e83d58874ba1de Andrey Smetanin 2015-07-03 @2185 int kvm_hv_hypercall(struct kvm_vcpu *vcpu) > e83d58874ba1de Andrey Smetanin 2015-07-03 2186 { > 4e62aa96d6e55c Vitaly Kuznetsov 2021-07-30 2187 struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu); > bd38b32053eb1c Siddharth Chandrasekaran 2021-05-26 2188 struct kvm_hv_hcall hc; > bd38b32053eb1c Siddharth Chandrasekaran 2021-05-26 2189 u64 ret = HV_STATUS_SUCCESS; ... but let me repeat myself: (see my previous reply here: https://lore.kernel.org/kvm/874jyw2v5n.fsf@redhat.com/) The source of the problem seems to be that Clang probably inlines kvm_hv_send_ipi() as on-stack variables in kvm_hv_hypercall() can not exceed 1024 bytes limit (struct kvm_hv_hcall is 144 bytes, the rest is negligible). The patch I mention above will likely fix the issue as it significantly reduces on-stack allocations in kvm_hv_send_ipi() but in this situation it shouldn't be inlined in the first place. (I still hope that I'm wrong finger pointing at the compiler here and someone smart will come to correct me :-) > e83d58874ba1de Andrey Smetanin 2015-07-03 2190 > e83d58874ba1de Andrey Smetanin 2015-07-03 2191 /* > e83d58874ba1de Andrey Smetanin 2015-07-03 2192 * hypercall generates UD from non zero cpl and real mode > e83d58874ba1de Andrey Smetanin 2015-07-03 2193 * per HYPER-V spec > e83d58874ba1de Andrey Smetanin 2015-07-03 2194 */ > b3646477d458fb Jason Baron 2021-01-14 2195 if (static_call(kvm_x86_get_cpl)(vcpu) != 0 || !is_protmode(vcpu)) { > e83d58874ba1de Andrey Smetanin 2015-07-03 2196 kvm_queue_exception(vcpu, UD_VECTOR); > 0d9c055eaaf41b Andrey Smetanin 2016-02-11 2197 return 1; > e83d58874ba1de Andrey Smetanin 2015-07-03 2198 } > e83d58874ba1de Andrey Smetanin 2015-07-03 2199 > > :::::: The code at line 2185 was first introduced by commit > :::::: e83d58874ba1de74c13d3c6b05f95a023c860d25 kvm/x86: move Hyper-V MSR's/hypercall code into hyperv.c file > > :::::: TO: Andrey Smetanin <asmetanin@virtuozzo.com> > :::::: CC: Paolo Bonzini <pbonzini@redhat.com> -- Vitaly ^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [stable:linux-5.15.y 5373/9027] arch/x86/kvm/hyperv.c:2185:5: warning: stack frame size (1036) exceeds limit (1024) in 'kvm_hv_hypercall' 2022-08-15 8:10 ` [stable:linux-5.15.y 5373/9027] arch/x86/kvm/hyperv.c:2185:5: warning: stack frame size (1036) exceeds limit (1024) in 'kvm_hv_hypercall' Vitaly Kuznetsov @ 2022-08-15 17:05 ` Nathan Chancellor 0 siblings, 0 replies; 2+ messages in thread From: Nathan Chancellor @ 2022-08-15 17:05 UTC (permalink / raw) To: Vitaly Kuznetsov Cc: kernel test robot, kvm, llvm, kbuild-all, linux-kernel, Greg Kroah-Hartman, Paolo Bonzini On Mon, Aug 15, 2022 at 10:10:07AM +0200, Vitaly Kuznetsov wrote: > kernel test robot <lkp@intel.com> writes: > > > Hi Vitaly, > > > > FYI, the error/warning still remains. > > > > Yes, this is expected as the patch which is supposed to 'fix' this is > still pendind. The latest version is here: > > https://lore.kernel.org/kvm/20220803134540.399220-1-vkuznets@redhat.com/ > > ... > > > tree: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git linux-5.15.y > > head: 7217df81279835a7aee62a07aabb7b8fb8c766f2 > > commit: cb188e07105f2216f5efbefac95df4b6ce266906 [5373/9027] KVM: x86: hyper-v: HVCALL_SEND_IPI_EX is an XMM fast hypercall > > config: i386-allmodconfig (https://download.01.org/0day-ci/archive/20220814/202208142025.NHKErAjq-lkp@intel.com/config) > > compiler: clang version 16.0.0 (https://github.com/llvm/llvm-project 52cd00cabf479aa7eb6dbb063b7ba41ea57bce9e) > > reproduce (this is a W=1 build): > > wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross > > chmod +x ~/bin/make.cross > > # https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?id=cb188e07105f2216f5efbefac95df4b6ce266906 > > git remote add stable https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git > > git fetch --no-tags stable linux-5.15.y > > git checkout cb188e07105f2216f5efbefac95df4b6ce266906 > > # save the config file > > mkdir build_dir && cp config build_dir/.config > > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=i386 SHELL=/bin/bash arch/x86/kvm/ > > > > If you fix the issue, kindly add following tag where applicable > > Reported-by: kernel test robot <lkp@intel.com> > > > > All warnings (new ones prefixed by >>): > > > >>> arch/x86/kvm/hyperv.c:2185:5: warning: stack frame size (1036) exceeds limit (1024) in 'kvm_hv_hypercall' [-Wframe-larger-than] > > int kvm_hv_hypercall(struct kvm_vcpu *vcpu) > > ^ > > 1 warning generated. > > > > > > vim +/kvm_hv_hypercall +2185 arch/x86/kvm/hyperv.c > > > > 4ad81a91119df7 Vitaly Kuznetsov 2021-05-21 2184 > > e83d58874ba1de Andrey Smetanin 2015-07-03 @2185 int kvm_hv_hypercall(struct kvm_vcpu *vcpu) > > e83d58874ba1de Andrey Smetanin 2015-07-03 2186 { > > 4e62aa96d6e55c Vitaly Kuznetsov 2021-07-30 2187 struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu); > > bd38b32053eb1c Siddharth Chandrasekaran 2021-05-26 2188 struct kvm_hv_hcall hc; > > bd38b32053eb1c Siddharth Chandrasekaran 2021-05-26 2189 u64 ret = HV_STATUS_SUCCESS; > > ... but let me repeat myself: (see my previous reply here: > https://lore.kernel.org/kvm/874jyw2v5n.fsf@redhat.com/) > The source of the problem seems to be that Clang probably inlines > kvm_hv_send_ipi() as on-stack variables in kvm_hv_hypercall() can not > exceed 1024 bytes limit (struct kvm_hv_hcall is 144 bytes, the rest is > negligible). The patch I mention above will likely fix the issue as it > significantly reduces on-stack allocations in kvm_hv_send_ipi() but in > this situation it shouldn't be inlined in the first place. I seem to recall Nick mentioning at some point that LLVM gives a massive inlining discount to functions that are only called once so I guess that would explain why kvm_hv_send_ipi() gets inlined into kvm_hv_hypercall(). I think there are some inlining cost flags we could experiment with to see if we can avoid inlining functions with high stack usage into other functions. Additionally, the configurations that reported this warning are allmodconfig and allyesconfig, which enable KASAN, which is known to use more stack usage with clang: https://github.com/ClangBuiltLinux/linux/issues/39 I am hoping we'll get to addressing that during our meet up right before Plumbers but we'll see. > (I still hope that I'm wrong finger pointing at the compiler here and > someone smart will come to correct me :-) Other folks more familiar with the LLVM side of things might correct me :) Cheers, Nathan ^ permalink raw reply [flat|nested] 2+ messages in thread
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2022-08-15 8:10 ` [stable:linux-5.15.y 5373/9027] arch/x86/kvm/hyperv.c:2185:5: warning: stack frame size (1036) exceeds limit (1024) in 'kvm_hv_hypercall' Vitaly Kuznetsov
2022-08-15 17:05 ` Nathan Chancellor
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