vmlinux.o: warning: objtool: __svm_sev_es_vcpu_run()+0x54: BP used as a scratch register

vmlinux.o: warning: objtool: __svm_sev_es_vcpu_run()+0x54: BP used as a scratch register

[kernel test robot]

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tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   8ab774587903771821b59471cc723bba6d893942
commit: 16809ecdc1e8ab7278f1d60021ac809edd17d060 KVM: SVM: Provide an updated VMRUN invocation for SEV-ES guests
date:   11 months ago
config: x86_64-buildonly-randconfig-r005-20211117 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=16809ecdc1e8ab7278f1d60021ac809edd17d060
        git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
        git fetch --no-tags linus master
        git checkout 16809ecdc1e8ab7278f1d60021ac809edd17d060
        # save the attached .config to linux build tree
        mkdir build_dir
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   vmlinux.o: warning: objtool: __do_fast_syscall_32()+0x3d: call to syscall_enter_from_user_mode_work() leaves .noinstr.text section
   vmlinux.o: warning: objtool: __svm_vcpu_run()+0x10e: BP used as a scratch register
>> vmlinux.o: warning: objtool: __svm_sev_es_vcpu_run()+0x54: BP used as a scratch register
   vmlinux.o: warning: objtool: do_machine_check()+0x93c: call to mce_panic.isra.0() leaves .noinstr.text section
   vmlinux.o: warning: objtool: match_held_lock()+0xcd: call to rcu_read_lock_any_held() leaves .noinstr.text section
   vmlinux.o: warning: objtool: lock_is_held_type()+0x67: call to check_flags.part.0() leaves .noinstr.text section

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

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Re: vmlinux.o: warning: objtool: __svm_sev_es_vcpu_run()+0x54: BP used as a scratch register

[Sean Christopherson]

On Wed, Nov 17, 2021, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   8ab774587903771821b59471cc723bba6d893942
> commit: 16809ecdc1e8ab7278f1d60021ac809edd17d060 KVM: SVM: Provide an updated VMRUN invocation for SEV-ES guests
> date:   11 months ago
> config: x86_64-buildonly-randconfig-r005-20211117 (attached as .config)
> compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
> reproduce (this is a W=1 build):
>         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=16809ecdc1e8ab7278f1d60021ac809edd17d060
>         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>         git fetch --no-tags linus master
>         git checkout 16809ecdc1e8ab7278f1d60021ac809edd17d060
>         # save the attached .config to linux build tree
>         mkdir build_dir
>         make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
> 
> All warnings (new ones prefixed by >>):
> 
>    vmlinux.o: warning: objtool: __do_fast_syscall_32()+0x3d: call to syscall_enter_from_user_mode_work() leaves .noinstr.text section
>    vmlinux.o: warning: objtool: __svm_vcpu_run()+0x10e: BP used as a scratch register
> >> vmlinux.o: warning: objtool: __svm_sev_es_vcpu_run()+0x54: BP used as a scratch register

__svm_vcpu_run() and __svm_sev_es_vcpu_run() PUSH/POP RBP but don't create a stack
frame, which triggers the objtool warning because objtool things the code is using
BP as a scratch register (obviously).  This shows up when CONFIG_FRAME_POINTER=y
and KVM AMD is built into the kernel (apparently 'objtool check' isn't run on modules?).

The easy fix to is add "mov %rsp, %rbp" to create a stack frame.  Kinda pointless
since neither function makes true calls to other functions, but the extra MOV is
harmless and it'd be nice to get rid of the objtool warning.