Re: [PATCH -v2] QEMU-KVM: MCE: Relay UCR MCE to guest

[Avi Kivity <avi@redhat.com>]

On 09/09/2009 05:28 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.
>
> v2:
>
> - Use qemu_ram_addr_from_host instead of self made one to covert from
>    host address to guest RAM address. Thanks Anthony Liguori.
>
>    

Patch looks good, but can you clarify the following:

> @@ -1877,12 +1995,20 @@ void kvm_hpet_enable_kpit(void)
>
>   int kvm_init_ap(void)
>   {
> +    struct sigaction action;
> +
>   #ifdef TARGET_I386
>       kvm_tpr_opt_setup();
>   #endif
>       qemu_add_vm_change_state_handler(kvm_vm_state_change_handler, NULL);
>
>       signal(SIG_IPI, sig_ipi_handler);
> +
> +    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;
>   }
>    

Why do we need a SIGBUS handler?  kvm vcpu threads will block and 
dequeue a SIGBUG in guest mode, so the handler will never be called, and 
we can't really handle SIGBUS in user mode.

(also, I if we can't handle guest-mode SIGBUS I think it would be nice 
to raise it again so the process terminates due to the SIGBUS).

-- 
error compiling committee.c: too many arguments to function