Re: [Qemu-ppc] [RFC PATCH v1 3/3] spapr: spapr: Work around the memory hotplug failure with DDW

[David Gibson]

On Fri, Jun 03, 2016 at 11:19:44AM +0530, Bharata B Rao wrote:
> Memory hotplug can fail for some combinations of RAM and maxmem when
> DDW is enabled in the presence of devices like nec-usb-xhci. DDW depends
> on maximum addressable memory returned by guest and this value is currently
> being calculated wrongly by the guest kernel routine memory_hotplug_max().
> While there is an attempt to fix the guest kernel, this patch works
> around the problem within QEMU itself.
> 
> memory_hotplug_max() routine in the guest kernel arrives at max
> addressable memory by multiplying lmb-size with the lmb-count obtained
> from ibm,dynamic-memory property. There are two assumptions here:
> 
> - All LMBs are part of ibm,dynamic memory: This is not true for PowerKVM
>   where only hot-pluggable LMBs are present in this property.
> - The memory area comprising of RAM and hotplug region is contiguous: This
>   needn't be true always for PowerKVM as there can be gap between
>   boot time RAM and hotplug region.
> 
> This work around involves having all the LMBs (RMA, rest of the boot time
> LMBs and hot-pluggable LMBs) as part of ibm,dynamic-memory so that
> guest kernel's calculation of max addressable memory comes out correct
> resulting in correct DDW value which prevents memory hotplug failures.
> address@hidden is created for RMA, but RMA LMBs are also represented as
> "reserved" LMBs in ibm,dynamic-memory. Parts of this are essenitally a
> revert of e8f986fc57a664a74b9f685b466506366a15201b.
> 
> In addition to this, the alignment of hotplug memory region is reduced from
> current 1G to 256M (LMB size in PowerKVM) so that we don't end up with any
> gaps between boot time RAM and hotplug region.

Hmm.. could we work around the problem without altering the memory
alignment by inserting extra dummy reserved LMBs covering the gap?

> 
> Signed-off-by: Bharata B Rao <address@hidden>
> ---
>  hw/ppc/spapr.c         | 59 
> +++++++++++++++++++++++++++++++++++---------------
>  include/hw/ppc/spapr.h |  5 +++--
>  2 files changed, 45 insertions(+), 19 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 623c35f..3dfbc37 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -569,7 +569,6 @@ static int spapr_populate_memory(sPAPRMachineState 
> *spapr, void *fdt)
>          }
>          if (!mem_start) {
>              /* ppc_spapr_init() checks for rma_size <= node0_size already */
> -            spapr_populate_memory_node(fdt, i, 0, spapr->rma_size);
>              mem_start += spapr->rma_size;
>              node_size -= spapr->rma_size;
>          }
> @@ -762,18 +761,13 @@ static int 
> spapr_populate_drconf_memory(sPAPRMachineState *spapr, void *fdt)
>      int ret, i, offset;
>      uint64_t lmb_size = SPAPR_MEMORY_BLOCK_SIZE;
>      uint32_t prop_lmb_size[] = {0, cpu_to_be32(lmb_size)};
> -    uint32_t nr_lmbs = (machine->maxram_size - machine->ram_size)/lmb_size;
> +    uint32_t nr_rma_lmbs = spapr->rma_size / lmb_size;
> +    uint32_t nr_lmbs = machine->maxram_size / lmb_size;
> +    uint32_t nr_assigned_lmbs = machine->ram_size / lmb_size;
>      uint32_t *int_buf, *cur_index, buf_len;
>      int nr_nodes = nb_numa_nodes ? nb_numa_nodes : 1;
>  
>      /*
> -     * Don't create the node if there are no DR LMBs.
> -     */
> -    if (!nr_lmbs) {
> -        return 0;
> -    }
> -
> -    /*
>       * Allocate enough buffer size to fit in ibm,dynamic-memory
>       * or ibm,associativity-lookup-arrays
>       */
> @@ -805,9 +799,15 @@ static int 
> spapr_populate_drconf_memory(sPAPRMachineState *spapr, void *fdt)
>      for (i = 0; i < nr_lmbs; i++) {
>          sPAPRDRConnector *drc;
>          sPAPRDRConnectorClass *drck;
> -        uint64_t addr = i * lmb_size + spapr->hotplug_memory.base;;
> +        uint64_t addr;
>          uint32_t *dynamic_memory = cur_index;
>  
> +        if (i < nr_assigned_lmbs) {
> +            addr = i * lmb_size;
> +        } else {
> +            addr = (i - nr_assigned_lmbs) * lmb_size +
> +                    spapr->hotplug_memory.base;
> +        }
>          drc = spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_LMB,
>                                         addr/lmb_size);
>          g_assert(drc);
> @@ -820,7 +820,11 @@ static int 
> spapr_populate_drconf_memory(sPAPRMachineState *spapr, void *fdt)
>          dynamic_memory[4] = cpu_to_be32(numa_get_node(addr, NULL));
>          if (addr < machine->ram_size ||
>                      memory_region_present(get_system_memory(), addr)) {
> -            dynamic_memory[5] = cpu_to_be32(SPAPR_LMB_FLAGS_ASSIGNED);
> +            if (i < nr_rma_lmbs) {
> +                dynamic_memory[5] = cpu_to_be32(SPAPR_LMB_FLAGS_RESERVED);
> +            } else {
> +                dynamic_memory[5] = cpu_to_be32(SPAPR_LMB_FLAGS_ASSIGNED);
> +            }
>          } else {
>              dynamic_memory[5] = cpu_to_be32(0);
>          }
> @@ -882,6 +886,8 @@ int spapr_h_cas_compose_response(sPAPRMachineState *spapr,
>      /* Generate ibm,dynamic-reconfiguration-memory node if required */
>      if (memory_update && smc->dr_lmb_enabled) {
>          _FDT((spapr_populate_drconf_memory(spapr, fdt)));
> +    } else {
> +        _FDT((spapr_populate_memory(spapr, fdt)));
>      }
>  
>      /* Pack resulting tree */
> @@ -919,10 +925,23 @@ static void spapr_finalize_fdt(sPAPRMachineState *spapr,
>      /* open out the base tree into a temp buffer for the final tweaks */
>      _FDT((fdt_open_into(spapr->fdt_skel, fdt, FDT_MAX_SIZE)));
>  
> -    ret = spapr_populate_memory(spapr, fdt);
> -    if (ret < 0) {
> -        fprintf(stderr, "couldn't setup memory nodes in fdt\n");
> -        exit(1);
> +    /*
> +     * Add address@hidden node to represent RMA. Rest of the memory is either
> +     * represented by memory nodes or ibm,dynamic-reconfiguration-memory
> +     * node later during ibm,client-architecture-support call.
> +     *
> +     * If NUMA is configured, ensure that address@hidden ends up in the
> +     * first memory-less node.
> +     */
> +    if (nb_numa_nodes) {
> +        for (i = 0; i < nb_numa_nodes; ++i) {
> +            if (numa_info[i].node_mem) {
> +                spapr_populate_memory_node(fdt, i, 0, spapr->rma_size);
> +                break;
> +            }
> +        }
> +    } else {
> +        spapr_populate_memory_node(fdt, 0, 0, spapr->rma_size);
>      }
>  
>      ret = spapr_populate_vdevice(spapr->vio_bus, fdt);
> @@ -1654,14 +1673,20 @@ static void 
> spapr_create_lmb_dr_connectors(sPAPRMachineState *spapr)
>  {
>      MachineState *machine = MACHINE(spapr);
>      uint64_t lmb_size = SPAPR_MEMORY_BLOCK_SIZE;
> -    uint32_t nr_lmbs = (machine->maxram_size - machine->ram_size)/lmb_size;
> +    uint32_t nr_lmbs = machine->maxram_size / lmb_size;
> +    uint32_t nr_assigned_lmbs = machine->ram_size / lmb_size;
>      int i;
>  
>      for (i = 0; i < nr_lmbs; i++) {
>          sPAPRDRConnector *drc;
>          uint64_t addr;
>  
> -        addr = i * lmb_size + spapr->hotplug_memory.base;
> +        if (i < nr_assigned_lmbs) {
> +            addr = i * lmb_size;
> +        } else {
> +            addr = (i - nr_assigned_lmbs) * lmb_size +
> +                    spapr->hotplug_memory.base;
> +        }
>          drc = spapr_dr_connector_new(OBJECT(spapr), 
> SPAPR_DR_CONNECTOR_TYPE_LMB,
>                                       addr/lmb_size);
>          qemu_register_reset(spapr_drc_reset, drc);
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index b2aeb15..e5ef979 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -619,9 +619,10 @@ int spapr_rng_populate_dt(void *fdt);
>  #define SPAPR_DR_LMB_LIST_ENTRY_SIZE 6
>  
>  /*
> - * This flag value defines the LMB as assigned in ibm,dynamic-memory
> - * property under ibm,dynamic-reconfiguration-memory node.
> + * Defines for flag value in ibm,dynamic-memory property under
> + * ibm,dynamic-reconfiguration-memory node.
>   */
>  #define SPAPR_LMB_FLAGS_ASSIGNED 0x00000008
> +#define SPAPR_LMB_FLAGS_RESERVED 0x00000080
>  
>  #endif /* !defined (__HW_SPAPR_H__) */

-- 
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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