Quoting Bharata B Rao (2016-06-07 21:35:54) > On Tue, Jun 07, 2016 at 06:37:28PM -0500, Michael Roth wrote: > > 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 <bhar...@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. > > Yes. > > > > > > - 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 > > Hmm I thought I got all such occurances covered :( > > > > > > + 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? > > Since kernel won't look at reserved LMBs, I thought it should be fine. > We could populate the addr, but we don't have DRC for them and hence > no DRC index, so anyway we will not have full information.
The 'DRC invalid' bit seems to suggests it's a perfectly valid scenario to have LMBs with no backing drc, so I would think the other fields should still be filled out appropriately, even if it might not get used by guest either way. I think an argument could be made for not setting addr for LMBs to used to cover the RAM->hotplug gap, since that's padding rather than real memory. But effectively re-using addr 0 seems like more of a liability than a safeguard. If 'reserved' flag is doing what we expect, then it's probably best not to deviate from normal values any more than necessary, IMO. > > > > > > + 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. > > Seems to work. I started with reserved based on Nathan's original > suggestion. > > So Nathan, which would be more appropriate here from kernel point of view ? > Reserved or 'DRC Invalid' ? Wouldn't we want an OR of both? > > Regards, > Bharata. >
