Quoting Bharata B Rao (2016-06-06 06:37:49)
> 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 <bhar...@linux.vnet.ibm.com>
> ---
> Changes in v2:
>
> - Dropped the patch that removed alignment gap b/n RAM and hotplug
> region, but instead populated ibm,dynamic-memory with LMBs represented
> as RESERVED for that gap. We create DRC objects for these LMBs
> as it simplifies the logic of populating ibm,dynamic-memory. There can
> at max be 4 such DRC objects for the gap area (1GB max) and hence it should
> be fine.
>
> v1: https://lists.gnu.org/archive/html/qemu-devel/2016-06/msg00627.html
>
> hw/ppc/spapr.c | 51
> ++++++++++++++++++++++++++++++++++++--------------
> include/hw/ppc/spapr.h | 5 +++--
> 2 files changed, 40 insertions(+), 16 deletions(-)
>
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 0636642..0f4f7a3 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -762,18 +762,14 @@ 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.
> - */
> - if (!nr_lmbs) {
> - return 0;
> - }
> -
> - /*
> * Allocate enough buffer size to fit in ibm,dynamic-memory
> * or ibm,associativity-lookup-arrays
> */
> @@ -805,11 +801,18 @@ 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 < hotplug_lmb_start) {
> + addr = i * lmb_size;
> + } else {
> + addr = (i - hotplug_lmb_start) * lmb_size +
> + spapr->hotplug_memory.base;
> + }
I think both cases reduce to addr = i * lmb_size
> +
> drc = spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_LMB,
> - addr/lmb_size);
> + addr / lmb_size);
> g_assert(drc);
> drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
>
> @@ -820,7 +823,14 @@ 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 (addr < spapr->rma_size) {
> + dynamic_memory[5] = cpu_to_be32(SPAPR_LMB_FLAGS_RESERVED);
> + } else {
> + dynamic_memory[5] = cpu_to_be32(SPAPR_LMB_FLAGS_ASSIGNED);
> + }
> + } else if (addr >= machine->ram_size &&
> + addr < spapr->hotplug_memory.base) {
> + dynamic_memory[5] = cpu_to_be32(SPAPR_LMB_FLAGS_RESERVED);
> } else {
> dynamic_memory[5] = cpu_to_be32(0);
> }
> @@ -1652,16 +1662,29 @@ static void spapr_drc_reset(void *opaque)
>
> 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 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;
> int i;
>
> for (i = 0; i < nr_lmbs; i++) {
> sPAPRDRConnector *drc;
> uint64_t addr;
>
> - addr = i * lmb_size + spapr->hotplug_memory.base;
> + /*
> + * Create DRC objects for entire memory range including RMA,
> boot-time
> + * memory and hotplug memory and for the gap b/n RAM and hotplug
> + * memory region.
> + */
> + if (i < hotplug_lmb_start) {
> + addr = i * lmb_size;
> + } else {
> + addr = (i - hotplug_lmb_start) * lmb_size +
> + spapr->hotplug_memory.base;
> + }
Here too
> +
> drc = spapr_dr_connector_new(OBJECT(spapr),
> SPAPR_DR_CONNECTOR_TYPE_LMB,
> addr/lmb_size);
And since there are no gaps, addr / lmb_size can now just be i, which I
guess means you don't need work with addr at all here anymore...
> qemu_register_reset(spapr_drc_reset, drc);
> 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
>
