Re: [Qemu-ppc] [PATCH 06/13] spapr/xive: fix migration of the XiveTCTX under TCG

[David Gibson]

On Mon, Jan 07, 2019 at 07:39:39PM +0100, Cédric Le Goater wrote:
> When the thread interrupt management state is retrieved from the KVM
> VCPU, word2 is saved under the QEMU XIVE thread context to print out
> the OS CAM line under the QEMU monitor.
> 
> This breaks the migration of a TCG guest (and with KVM when
> kernel_irqchip=off) because the matching algorithm of the presenter
> relies on the OS CAM value. Fix with an extra reset of the thread
> contexts to restore the expected value.
> 
> Signed-off-by: Cédric Le Goater <address@hidden>

Why is the CAM value you get from KVM different from the one you
expect in qemu?

> ---
>  hw/ppc/spapr_irq.c | 26 +++++++++++++++++++++++++-
>  1 file changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/ppc/spapr_irq.c b/hw/ppc/spapr_irq.c
> index 233c97c5ecd9..ba27d9d8e972 100644
> --- a/hw/ppc/spapr_irq.c
> +++ b/hw/ppc/spapr_irq.c
> @@ -363,7 +363,31 @@ static void 
> spapr_irq_cpu_intc_create_xive(sPAPRMachineState *spapr,
>  
>  static int spapr_irq_post_load_xive(sPAPRMachineState *spapr, int version_id)
>  {
> -    return spapr_xive_post_load(spapr->xive, version_id);
> +    CPUState *cs;
> +    int ret;
> +
> +    ret = spapr_xive_post_load(spapr->xive, version_id);
> +    if (ret) {
> +        return ret;
> +    }
> +
> +    /*
> +     * When the states are collected from the KVM XIVE device, word2
> +     * of the XiveTCTX is set to print out the OS CAM line under the
> +     * QEMU monitor.
> +     *
> +     * This breaks the migration on a TCG guest (or on KVM with
> +     * kernel_irqchip=off) because the matching algorithm of the
> +     * presenter relies on the OS CAM value. Fix with an extra reset
> +     * of the thread contexts to restore the expected value.
> +     */
> +    CPU_FOREACH(cs) {
> +        PowerPCCPU *cpu = POWERPC_CPU(cs);
> +
> +        /* (TCG) Set the OS CAM line of the thread interrupt context. */
> +        spapr_xive_set_tctx_os_cam(cpu->tctx);
> +    }
> +    return 0;
>  }
>  
>  static void spapr_irq_reset_xive(sPAPRMachineState *spapr, Error **errp)

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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