Re: [PATCH REPOST] spapr: Allow memory unplug to always succeed

[David Gibson]

On Mon, Dec 14, 2020 at 11:05:50AM +0100, Greg Kurz wrote:
65;6201;1c> It is currently impossible to hot-unplug a memory device between
> machine reset and CAS.
> 
> (qemu) device_del dimm1
> Error: Memory hot unplug not supported for this guest
> 
> This limitation was introduced in order to provide an explicit
> error path for older guests that didn't support hot-plug event
> sources (and thus memory hot-unplug).
> 
> The linux kernel has been supporting these since 4.11. All recent
> enough guests are thus capable of handling the removal of a memory
> device at all time, including during early boot.
> 
> Lift the limitation for the latest machine type. This means that
> trying to unplug memory from a guest that doesn't support it will
> likely just do nothing and the memory will only get removed at
> next reboot. Such older guests can still get the existing behavior
> by using an older machine type.
> 
> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---
> This patch was initially posted before the compat machine types
> for 6.0 got merged upstream. During the same period, David was
> also transitioning from github to gitlab, and the patch didn't
> applied cleanly. Now it does. Just reposting it unchanged for
> convenience.

Applied to ppc-for-6.0, thanks.

> ---
>  hw/ppc/spapr.c         |    6 +++++-
>  hw/ppc/spapr_events.c  |    3 ++-
>  include/hw/ppc/spapr.h |    1 +
>  3 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index dee48a0043bb..481c800a5a33 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -4051,7 +4051,8 @@ static void 
> spapr_machine_device_unplug_request(HotplugHandler *hotplug_dev,
>      SpaprMachineClass *smc = SPAPR_MACHINE_CLASS(mc);
>  
>      if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
> -        if (spapr_ovec_test(sms->ov5_cas, OV5_HP_EVT)) {
> +        if (!smc->pre_6_0_memory_unplug ||
> +            spapr_ovec_test(sms->ov5_cas, OV5_HP_EVT)) {
>              spapr_memory_unplug_request(hotplug_dev, dev, errp);
>          } else {
>              /* NOTE: this means there is a window after guest reset, prior to
> @@ -4537,8 +4538,11 @@ DEFINE_SPAPR_MACHINE(6_0, "6.0", true);
>   */
>  static void spapr_machine_5_2_class_options(MachineClass *mc)
>  {
> +    SpaprMachineClass *smc = SPAPR_MACHINE_CLASS(mc);
> +
>      spapr_machine_6_0_class_options(mc);
>      compat_props_add(mc->compat_props, hw_compat_5_2, hw_compat_5_2_len);
> +    smc->pre_6_0_memory_unplug = true;
>  }
>  
>  DEFINE_SPAPR_MACHINE(5_2, "5.2", false);
> diff --git a/hw/ppc/spapr_events.c b/hw/ppc/spapr_events.c
> index 3f37b49fd8ad..6aedd988b3d0 100644
> --- a/hw/ppc/spapr_events.c
> +++ b/hw/ppc/spapr_events.c
> @@ -658,7 +658,8 @@ static void spapr_hotplug_req_event(uint8_t hp_id, 
> uint8_t hp_action,
>          /* we should not be using count_indexed value unless the guest
>           * supports dedicated hotplug event source
>           */
> -        g_assert(spapr_ovec_test(spapr->ov5_cas, OV5_HP_EVT));
> +        g_assert(!SPAPR_MACHINE_GET_CLASS(spapr)->pre_6_0_memory_unplug ||
> +                 spapr_ovec_test(spapr->ov5_cas, OV5_HP_EVT));
>          hp->drc_id.count_indexed.count =
>              cpu_to_be32(drc_id->count_indexed.count);
>          hp->drc_id.count_indexed.index =
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index e0f10f252c08..06a5b4259f20 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -139,6 +139,7 @@ struct SpaprMachineClass {
>      hwaddr rma_limit;          /* clamp the RMA to this size */
>      bool pre_5_1_assoc_refpoints;
>      bool pre_5_2_numa_associativity;
> +    bool pre_6_0_memory_unplug;
>  
>      bool (*phb_placement)(SpaprMachineState *spapr, uint32_t index,
>                            uint64_t *buid, hwaddr *pio, 
> 
> 

-- 
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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