Re: [PATCH -v4] QEMU-KVM: MCE: Relay UCR MCE to guest

[Avi Kivity <avi@redhat.com>]

On 09/22/2009 04:12 AM, Huang Ying wrote:
> On Mon, 2009-09-21 at 18:08 +0800, Avi Kivity wrote:
>    
>> On 09/21/2009 05:43 AM, Huang Ying wrote:
>>      
>>> UCR (uncorrected recovery) MCE is supported in recent Intel CPUs,
>>> where some hardware error such as some memory error can be reported
>>> without PCC (processor context corrupted). To recover from such MCE,
>>> the corresponding memory will be unmapped, and all processes accessing
>>> the memory will be killed via SIGBUS.
>>>
>>> For KVM, if QEMU/KVM is killed, all guest processes will be killed
>>> too. So we relay SIGBUS from host OS to guest system via a UCR MCE
>>> injection. Then guest OS can isolate corresponding memory and kill
>>> necessary guest processes only. SIGBUS sent to main thread (not VCPU
>>> threads) will be broadcast to all VCPU threads as UCR MCE.
>>>
>>>
>>>
>>> --- a/qemu-kvm.c
>>> +++ b/qemu-kvm.c
>>> @@ -27,10 +27,23 @@
>>>    #include<sys/mman.h>
>>>    #include<sys/ioctl.h>
>>>    #include<signal.h>
>>> +#include<sys/signalfd.h>
>>>
>>>        
>> This causes a build failure, since not all hosts have<sys/signalfd.h>,
>> but more importantly:
>>      
> Maybe we can just add necessary fields to struct qemu_signalfd_siginfo.
> But this may be not portable.
>    

That is what I did.

>>> +
>>> +static void sigbus_handler(int n, struct signalfd_siginfo *siginfo, void *ctx)
>>> +{
>>>
>>>        
>> Here you accept signalfd_siginfo, while
>>
>>      
>>> +
>>> +    memset(&action, 0, sizeof(action));
>>> +    action.sa_flags = SA_SIGINFO;
>>> +    action.sa_sigaction = (void (*)(int, siginfo_t*, void*))sigbus_handler;
>>> +    sigaction(SIGBUS,&action, NULL);
>>> +    prctl(PR_MCE_KILL, 1, 1);
>>>        return 0;
>>>
>>>        
>> here you arm the function with something that will send it a siginfo_t.
>> So it looks like this is broken if a signal is ever received directly?
>> But can this happen due to signalfd?
>>      
> Because SIGBUS is blocked, I think the signal handler will not be called
> directly, but from sigfd_handler.
>    

Yes, I think so too.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.