Subject: Re: [PATCH v4 2/2] powerpc/pseries: Implement indexed-count hotplug memory remove

From: Michael Roth <[email-masked]>
Date: Tue, 23 Aug 2016 18:03:14 -0500

Quoting Sahil Mehta (2016-08-01 12:23:16)
> Indexed-count remove for memory hotplug guarantees that a contiguous block
> of <count> lmbs beginning at a specified <index> will be unassigned (NOT
> that <count> lmbs will be removed). Because of Qemu's per-DIMM memory
> management, the removal of a contiguous block of memory currently
> requires a series of individual calls. Indexed-count remove reduces
> this series into a single call.
> 
> Signed-off-by: Sahil Mehta <[email-masked]>
> ---
> v2:     -use u32s drc_index and count instead of u32 ic[]
>          in dlpar_memory
> v3:     -add logic to handle invalid drc_index input
> v4:     -none
> 
>  arch/powerpc/platforms/pseries/hotplug-memory.c |   90 +++++++++++++++++++++++
>  1 file changed, 90 insertions(+)
> 
> diff --git a/arch/powerpc/platforms/pseries/hotplug-memory.c b/arch/powerpc/platforms/pseries/hotplug-memory.c
> index 2d4ceb3..dd5eb38 100644
> --- a/arch/powerpc/platforms/pseries/hotplug-memory.c
> +++ b/arch/powerpc/platforms/pseries/hotplug-memory.c
> @@ -503,6 +503,92 @@ static int dlpar_memory_remove_by_index(u32 drc_index, struct property *prop)
>         return rc;
>  }
> 
> +static int dlpar_memory_remove_by_ic(u32 lmbs_to_remove, u32 drc_index,
> +                                    struct property *prop)
> +{
> +       struct of_drconf_cell *lmbs;
> +       u32 num_lmbs, *p;
> +       int i, rc, start_lmb_found;
> +       int lmbs_available = 0, start_index = 0, end_index;
> +
> +       pr_info("Attempting to hot-remove %u LMB(s) at %x\n",
> +               lmbs_to_remove, drc_index);
> +
> +       if (lmbs_to_remove == 0)
> +               return -EINVAL;
> +
> +       p = prop->value;
> +       num_lmbs = *p++;
> +       lmbs = (struct of_drconf_cell *)p;
> +       start_lmb_found = 0;
> +
> +       /* Navigate to drc_index */
> +       while (start_index < num_lmbs) {
> +               if (lmbs[start_index].drc_index == drc_index) {
> +                       start_lmb_found = 1;
> +                       break;
> +               }
> +
> +               start_index++;
> +       }
> +
> +       if (!start_lmb_found)
> +               return -EINVAL;
> +
> +       end_index = start_index + lmbs_to_remove;
> +
> +       /* Validate that there are enough LMBs to satisfy the request */
> +       for (i = start_index; i < end_index; i++) {
> +               if (lmbs[i].flags & DRCONF_MEM_RESERVED)
> +                       break;
> +
> +               lmbs_available++;
> +       }
> +
> +       if (lmbs_available < lmbs_to_remove)
> +               return -EINVAL;
> +
> +       for (i = 0; i < end_index; i++) {

Shouldn't this be i = start_index? Otherwise it seems we'd attempt to
satisfy the request using LMBs outside of the requested range.

> +               if (!(lmbs[i].flags & DRCONF_MEM_ASSIGNED))
> +                       continue;
> +
> +               rc = dlpar_remove_lmb(&lmbs[i]);
> +               if (rc)
> +                       break;
> +
> +               lmbs[i].reserved = 1;
> +       }
> +
> +       if (rc) {
> +               pr_err("Memory indexed-count-remove failed, adding any removed LMBs\n");
> +
> +               for (i = start_index; i < end_index; i++) {
> +                       if (!lmbs[i].reserved)
> +                               continue;
> +
> +                       rc = dlpar_add_lmb(&lmbs[i]);
> +                       if (rc)
> +                               pr_err("Failed to add LMB, drc index %x\n",
> +                                      be32_to_cpu(lmbs[i].drc_index));
> +
> +                       lmbs[i].reserved = 0;
> +               }
> +               rc = -EINVAL;
> +       } else {
> +               for (i = start_index; i < end_index; i++) {
> +                       if (!lmbs[i].reserved)
> +                               continue;
> +
> +                       pr_info("Memory at %llx (drc index %x) was hot-removed\n",
> +                               lmbs[i].base_addr, lmbs[i].drc_index);
> +
> +                       lmbs[i].reserved = 0;
> +               }
> +       }
> +
> +       return rc;
> +}
> +
>  #else
>  static inline int pseries_remove_memblock(unsigned long base,
>                                           unsigned int memblock_size)
> @@ -829,6 +915,10 @@ int dlpar_memory(struct pseries_hp_errorlog *hp_elog)
>                 } else if (hp_elog->id_type == PSERIES_HP_ELOG_ID_DRC_INDEX) {
>                         drc_index = hp_elog->_drc_u.drc_index;
>                         rc = dlpar_memory_remove_by_index(drc_index, prop);
> +               } else if (hp_elog->id_type == PSERIES_HP_ELOG_ID_DRC_IC) {
> +                       count = hp_elog->_drc_u.indexed_count[0];
> +                       drc_index = hp_elog->_drc_u.indexed_count[1];
> +                       rc = dlpar_memory_remove_by_ic(count, drc_index, prop);
>                 } else {
>                         rc = -EINVAL;
>                 }
> 
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