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SubjectRe: [PATCH v2] KVM: X86: Fix softlockup when get the current kvmclock timestamp
2017-11-25 11:14 GMT+08:00 kbuild test robot <lkp@intel.com>:
> Hi,
>
> Thank you for the patch! Perhaps something to improve:
>
> [auto build test WARNING on kvm/linux-next]
> [also build test WARNING on v4.14 next-20171124]
> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

Don't worry, the version which has already been merged doesn't have this issue.

Regards,
Wanpeng Li

>
> url: https://github.com/0day-ci/linux/commits/Wanpeng-Li/KVM-X86-Fix-softlockup-when-get-the-current-kvmclock-timestamp/20171109-030841
> base: https://git.kernel.org/pub/scm/virt/kvm/kvm.git linux-next
> config: i386-allyesconfig (attached as .config)
> compiler: gcc-7 (Debian 7.2.0-12) 7.2.1 20171025
> reproduce:
> # save the attached .config to linux build tree
> make ARCH=i386
>
> Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
> http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings
>
> All warnings (new ones prefixed by >>):
>
> In file included from arch/x86/kvm/x86.h:7:0,
> from arch/x86/kvm/x86.c:28:
> arch/x86/kvm/x86.c: In function 'get_kvmclock_ns':
>>> arch/x86/include/asm/pvclock.h:93:15: warning: '*((void *)&hv_clock+28)' may be used uninitialized in this function [-Wmaybe-uninitialized]
> u64 offset = pvclock_scale_delta(delta, src->tsc_to_system_mul,
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> src->tsc_shift);
> ~~~~~~~~~~~~~~~
> arch/x86/kvm/x86.c:1785:32: note: '*((void *)&hv_clock+28)' was declared here
> struct pvclock_vcpu_time_info hv_clock;
> ^~~~~~~~
> In file included from arch/x86/kvm/x86.h:7:0,
> from arch/x86/kvm/x86.c:28:
> arch/x86/include/asm/pvclock.h:65:2: warning: '*((void *)&hv_clock+24)' may be used uninitialized in this function [-Wmaybe-uninitialized]
> __asm__ (
> ^~~~~~~
> arch/x86/kvm/x86.c:1785:32: note: '*((void *)&hv_clock+24)' was declared here
> struct pvclock_vcpu_time_info hv_clock;
> ^~~~~~~~
> --
> In file included from arch/x86//kvm/x86.h:7:0,
> from arch/x86//kvm/x86.c:28:
> arch/x86//kvm/x86.c: In function 'get_kvmclock_ns':
>>> arch/x86/include/asm/pvclock.h:93:15: warning: '*((void *)&hv_clock+28)' may be used uninitialized in this function [-Wmaybe-uninitialized]
> u64 offset = pvclock_scale_delta(delta, src->tsc_to_system_mul,
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> src->tsc_shift);
> ~~~~~~~~~~~~~~~
> arch/x86//kvm/x86.c:1785:32: note: '*((void *)&hv_clock+28)' was declared here
> struct pvclock_vcpu_time_info hv_clock;
> ^~~~~~~~
> In file included from arch/x86//kvm/x86.h:7:0,
> from arch/x86//kvm/x86.c:28:
> arch/x86/include/asm/pvclock.h:65:2: warning: '*((void *)&hv_clock+24)' may be used uninitialized in this function [-Wmaybe-uninitialized]
> __asm__ (
> ^~~~~~~
> arch/x86//kvm/x86.c:1785:32: note: '*((void *)&hv_clock+24)' was declared here
> struct pvclock_vcpu_time_info hv_clock;
> ^~~~~~~~
>
> vim +93 arch/x86/include/asm/pvclock.h
>
> 347bb4448 Zachary Amsden 2010-08-19 88
> dce2db0a3 Marcelo Tosatti 2012-11-27 89 static __always_inline
> a5a1d1c29 Thomas Gleixner 2016-12-21 90 u64 __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src, u64 tsc)
> dce2db0a3 Marcelo Tosatti 2012-11-27 91 {
> 108b249c4 Paolo Bonzini 2016-09-01 92 u64 delta = tsc - src->tsc_timestamp;
> a5a1d1c29 Thomas Gleixner 2016-12-21 @93 u64 offset = pvclock_scale_delta(delta, src->tsc_to_system_mul,
> f7550d076 Minfei Huang 2016-05-27 94 src->tsc_shift);
> 3aed64f6d Paolo Bonzini 2016-06-09 95 return src->system_time + offset;
> dce2db0a3 Marcelo Tosatti 2012-11-27 96 }
> dce2db0a3 Marcelo Tosatti 2012-11-27 97
>
> :::::: The code at line 93 was first introduced by commit
> :::::: a5a1d1c2914b5316924c7893eb683a5420ebd3be clocksource: Use a plain u64 instead of cycle_t
>
> :::::: TO: Thomas Gleixner <tglx@linutronix.de>
> :::::: CC: Thomas Gleixner <tglx@linutronix.de>
>
> ---
> 0-DAY kernel test infrastructure Open Source Technology Center
> https://lists.01.org/pipermail/kbuild-all Intel Corporation

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