On 2011-01-17 08:31, Huang Ying wrote: > On Mon, 2011-01-17 at 15:11 +0800, Jan Kiszka wrote: >> On 2011-01-17 01:54, Huang Ying wrote: >>> On Sat, 2011-01-15 at 17:00 +0800, Jan Kiszka wrote: >>>> From: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> >>>> >>>> This case is a pure user space error we do not need to record. Moreover, >>>> it can be misused to flood the kernel log. Remove it. >>> >>> I don't think this is a pure user space error. This happens on real >>> hardware too, if the Machine Check exception is raised during early boot >>> stage or the second MC exception is raised before the first MC exception >>> is processed/cleared. >>> >>> So I use printk here to help debugging these issues. >>> >>> To avoid flooding the kernel log, we can use ratelimit. >> >> With user space I meant qemu, and maybe "error" was the wrong term. This >> code path is only triggered if qemu decides to. > > Not only decided by qemu, but also decided by guest OS. If guest OS > does not clear the MSR or guest OS does not set the X86_CR4_MCE bit in > the cr4, the triple fault will be triggered. Right, but qemu has full access to the state and can detect this. > >> And there you may also >> print this event (and you already do). > > Sorry, which print do you mean? I can not find similar print in user > space. Err, it's not yet there for the kvm case, I was starring at the tcg code path. > >> Another reason to not rely on catching this case here: KVM_X86_SET_MCE >> is obsolete on current kernels. Qemu will use a combination of >> KVM_SET_MSRS and KVM_SET_VCPU_EVENTS in the future, only falling back to >> this interface on pre-vcpu-events kernels. Then you need to debug this >> in user space anyway as the triple fault will no longer make it to the >> kernel. > > OK. Then, I think it will be helpful for debugging if we can print > something like this in user space implementation. qemu_log_mask(CPU_LOG_RESET, "Triple fault\n"); (and there will be a message on the monitor if raised manually) Jan
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