Re: [for-5.0 1/4] spapr: Don't trigger a CAS reboot for XICS/XIVE mode changeover

[Cédric Le Goater]

On 29/11/2019 06:33, David Gibson wrote:
> PAPR allows the interrupt controller used on a POWER9 machine (XICS or
> XIVE) to be selected by the guest operating system, by using the
> ibm,client-architecture-support (CAS) feature negotiation call.
> 
> Currently, if the guest selects an interrupt controller different from the
> one selected at initial boot, this causes the system to be reset with the
> new model and the boot starts again.  This means we run through the SLOF
> boot process twice, as well as any other bootloader (e.g. grub) in use
> before the OS calls CAS.  This can be confusing and/or inconvenient for
> users.
> 
> Thanks to two fairly recent changes, we no longer need this reboot.  1) we
> now completely regenerate the device tree when CAS is called (meaning we
> don't need special case updates for all the device tree changes caused by
> the interrupt controller mode change),  2) we now have explicit code paths
> to activate and deactivate the different interrupt controllers, rather than
> just implicitly calling those at machine reset time.
> 
> We can therefore eliminate the reboot for changing irq mode, simply by
> putting a called to spapr_irq_update_active_intc() before we call
> spapr_h_cas_compose_response() (which gives the updated device tree to the
> guest firmware and OS).
> 
> Signed-off-by: David Gibson <address@hidden>


Reviewed-by: Cedric Le Goater <address@hidden>

> ---
>  hw/ppc/spapr_hcall.c | 33 +++++++++++++--------------------
>  1 file changed, 13 insertions(+), 20 deletions(-)
> 
> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> index 140f05c1c6..05a7ca275b 100644
> --- a/hw/ppc/spapr_hcall.c
> +++ b/hw/ppc/spapr_hcall.c
> @@ -1767,21 +1767,10 @@ static target_ulong 
> h_client_architecture_support(PowerPCCPU *cpu,
>      }
>      spapr->cas_pre_isa3_guest = !spapr_ovec_test(ov1_guest, OV1_PPC_3_00);
>      spapr_ovec_cleanup(ov1_guest);
> -    if (!spapr->cas_reboot) {
> -        /* If spapr_machine_reset() did not set up a HPT but one is necessary
> -         * (because the guest isn't going to use radix) then set it up here. 
> */
> -        if ((spapr->patb_entry & PATE1_GR) && !guest_radix) {
> -            /* legacy hash or new hash: */
> -            spapr_setup_hpt_and_vrma(spapr);
> -        }
> -        spapr->cas_reboot =
> -            (spapr_h_cas_compose_response(spapr, args[1], args[2],
> -                                          ov5_updates) != 0);
> -    }
>  
>      /*
> -     * Ensure the guest asks for an interrupt mode we support; otherwise
> -     * terminate the boot.
> +     * Ensure the guest asks for an interrupt mode we support;
> +     * otherwise terminate the boot.
>       */
>      if (guest_xive) {
>          if (!spapr->irq->xive) {
> @@ -1797,14 +1786,18 @@ static target_ulong 
> h_client_architecture_support(PowerPCCPU *cpu,
>          }
>      }
>  
> -    /*
> -     * Generate a machine reset when we have an update of the
> -     * interrupt mode. Only required when the machine supports both
> -     * modes.
> -     */
> +    spapr_irq_update_active_intc(spapr);
> +
>      if (!spapr->cas_reboot) {
> -        spapr->cas_reboot = spapr_ovec_test(ov5_updates, OV5_XIVE_EXPLOIT)
> -            && spapr->irq->xics && spapr->irq->xive;
> +        /* If spapr_machine_reset() did not set up a HPT but one is necessary
> +         * (because the guest isn't going to use radix) then set it up here. 
> */
> +        if ((spapr->patb_entry & PATE1_GR) && !guest_radix) {
> +            /* legacy hash or new hash: */
> +            spapr_setup_hpt_and_vrma(spapr);
> +        }
> +        spapr->cas_reboot =
> +            (spapr_h_cas_compose_response(spapr, args[1], args[2],
> +                                          ov5_updates) != 0);
>      }
>  
>      spapr_ovec_cleanup(ov5_updates);
>