Re: [Qemu-devel] [PATCH v3] spapr: Ensure all LMBs are represented in ibm, dynamic-memory

[Michael Roth <mdroth@linux.vnet.ibm.com>]

Quoting Bharata B Rao (2016-06-07 00:19:03)
> 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.
> 
> To work around this guest kernel bug, ensure that ibm,dynamic-memory
> has information about all the LMBs (RMA, boot-time LMBs, future
> hotpluggable LMBs, and dummy LMBs to cover the gap between RAM and
> hotpluggable region).
> 
> RMA is represented separately by memory@0 node. Hence mark RMA LMBs
> and also the LMBs for the gap b/n RAM and hotpluggable region as
> reserved so that these LMBs are not recounted/counted by guest.
> 
> Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> ---
> Changes in v3:
> 
> - Not touching spapr_create_lmb_dr_connectors() so that we continue
>   to have DRC objects for only hotpluggable LMBs.
> - Simplified the logic of creating dynamic-memory node based on comments
>   from Michael Roth and David Gibson.
> 
> v2: https://lists.gnu.org/archive/html/qemu-devel/2016-06/msg01316.html
> 
>  hw/ppc/spapr.c         | 51 ++++++++++++++++++++++++++++++++------------------
>  include/hw/ppc/spapr.h |  5 +++--
>  2 files changed, 36 insertions(+), 20 deletions(-)
> 
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 0636642..9d1d43d 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -762,14 +762,17 @@ 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 hotplug_lmb_start = spapr->hotplug_memory.base / lmb_size;
> +    uint32_t nr_lmbs = (spapr->hotplug_memory.base +
> +                       memory_region_size(&spapr->hotplug_memory.mr)) /
> +                       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.
> +     * Don't create the node if there is no hotpluggable memory
>       */
> -    if (!nr_lmbs) {
> +    if (machine->ram_size == machine->maxram_size) {
>          return 0;
>      }
> 
> @@ -805,24 +808,36 @@ static int spapr_populate_drconf_memory(sPAPRMachineState *spapr, void *fdt)
>      for (i = 0; i < nr_lmbs; i++) {
>          sPAPRDRConnector *drc;
>          sPAPRDRConnectorClass *drck;

Since these ^ are only used if (i >= hotplug_lmb_start), it might be
clearer to move them there now.

> -        uint64_t addr = i * lmb_size + spapr->hotplug_memory.base;;
> +        uint64_t addr = i * lmb_size;
>          uint32_t *dynamic_memory = cur_index;
> 
> -        drc = spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_LMB,
> -                                       addr/lmb_size);
> -        g_assert(drc);
> -        drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
> -
> -        dynamic_memory[0] = cpu_to_be32(addr >> 32);
> -        dynamic_memory[1] = cpu_to_be32(addr & 0xffffffff);
> -        dynamic_memory[2] = cpu_to_be32(drck->get_index(drc));
> -        dynamic_memory[3] = cpu_to_be32(0); /* reserved */
> -        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 >= hotplug_lmb_start) {
> +            drc = spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_LMB,
> +                                           addr / lmb_size);

Could just be i

> +            g_assert(drc);
> +            drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
> +
> +            dynamic_memory[0] = cpu_to_be32(addr >> 32);
> +            dynamic_memory[1] = cpu_to_be32(addr & 0xffffffff);
> +            dynamic_memory[2] = cpu_to_be32(drck->get_index(drc));
> +            dynamic_memory[3] = cpu_to_be32(0); /* reserved */
> +            dynamic_memory[4] = cpu_to_be32(numa_get_node(addr, NULL));
> +            if (memory_region_present(get_system_memory(), addr)) {
> +                dynamic_memory[5] = cpu_to_be32(SPAPR_LMB_FLAGS_ASSIGNED);
> +            } else {
> +                dynamic_memory[5] = cpu_to_be32(0);
> +            }
>          } else {
> -            dynamic_memory[5] = cpu_to_be32(0);
> +            /*
> +             * LMB information for RMA, boot time RAM and gap b/n RAM and
> +             * hotplug memory region -- all these are marked as reserved.
> +             */
> +            dynamic_memory[0] = cpu_to_be32(0);
> +            dynamic_memory[1] = cpu_to_be32(0);

Are we sure we shouldn't still encode the addr here?

> +            dynamic_memory[2] = cpu_to_be32(0);
> +            dynamic_memory[3] = cpu_to_be32(0); /* reserved */
> +            dynamic_memory[4] = cpu_to_be32(-1);
> +            dynamic_memory[5] = cpu_to_be32(SPAPR_LMB_FLAGS_RESERVED);

LoPAPR Table 248 defines a "DRC invalid" bit at 0x00000020, which I
think is what we'll want for cases where there's no backing DRC.

>          }
> 
>          cur_index += SPAPR_DR_LMB_LIST_ENTRY_SIZE;
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index 971df3d..bb265a2 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -620,9 +620,10 @@ 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__) */
> -- 
> 2.1.0
>