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

[Avi Kivity <avi@redhat.com>]

On 09/07/2009 11:32 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.
>
>    

Won't the guest be confused by the broadcast?  How does real hardware work?
>
> +static void sigbus_handler(int n, struct signalfd_siginfo *siginfo, void *ctx)
> +{
> +    if (siginfo->ssi_code == BUS_MCEERR_AO) {
> +        uint64_t status;
> +        unsigned long paddr;
> +        CPUState *cenv;
> +
> +        /* Hope we are lucky for AO MCE */
> +        if (kvm_addr_userspace_to_phys((unsigned long)siginfo->ssi_addr,
> +&paddr)) {
> +            fprintf(stderr, "Hardware memory error for memory used by "
> +                    "QEMU itself instead of guest system!: %llx\n",
> +                    (unsigned long long)siginfo->ssi_addr);
> +            return;
> +        }
> +        status = MCI_STATUS_VAL | MCI_STATUS_UC | MCI_STATUS_EN
> +            | MCI_STATUS_MISCV | MCI_STATUS_ADDRV | MCI_STATUS_S
> +            | 0xc0;
> +        kvm_inject_x86_mce(first_cpu, 9, status,
> +                           MCG_STATUS_MCIP | MCG_STATUS_RIPV, paddr,
> +                           (MCM_ADDR_PHYS<<  6) | 0xc);
>    

This is a vcpu ioctl, yes?  if so it must be called from the vcpu thread.

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