qemu/hw/ppc
David Gibson 8897ea5a9f spapr: Don't attempt to clamp RMA to VRMA constraint
The Real Mode Area (RMA) is the part of memory which a guest can access
when in real (MMU off) mode.  Of course, for a guest under KVM, the MMU
isn't really turned off, it's just in a special translation mode - Virtual
Real Mode Area (VRMA) - which looks like real mode in guest mode.

The mechanics of how this works when using the hash MMU (HPT) put a
constraint on the size of the RMA, which depends on the size of the
HPT.  So, the latter part of spapr_setup_hpt_and_vrma() clamps the RMA
we advertise to the guest based on this VRMA limit.

There are several things wrong with this:
 1) spapr_setup_hpt_and_vrma() doesn't actually clamp, it takes the minimum
    of Node 0 memory size and the VRMA limit.  That will *often* work the
    same as clamping, but there can be other constraints on RMA size which
    supersede Node 0 memory size.  We have real bugs caused by this
    (currently worked around in the guest kernel)
 2) Some callers of spapr_setup_hpt_and_vrma() are in a situation where
    we're past the point that we can actually advertise an RMA limit to the
    guest
 3) But most fundamentally, the VRMA limit depends on host configuration
    (page size) which shouldn't be visible to the guest, but this partially
    exposes it.  This can cause problems with migration in certain edge
    cases, although we will mostly get away with it.

In practice, this clamping is almost never applied anyway.  With 64kiB
pages and the normal rules for sizing of the HPT, the theoretical VRMA
limit will be 4x(guest memory size) and so never hit.  It will hit with
4kiB pages, where it will be (guest memory size)/4.  However all mainstream
distro kernels for POWER have used a 64kiB page size for at least 10 years.

So, simply replace this logic with a check that the RMA we've calculated
based only on guest visible configuration will fit within the host implied
VRMA limit.  This can break if running HPT guests on a host kernel with
4kiB page size.  As noted that's very rare.  There also exist several
possible workarounds:
  * Change the host kernel to use 64kiB pages
  * Use radix MMU (RPT) guests instead of HPT
  * Use 64kiB hugepages on the host to back guest memory
  * Increase the guest memory size so that the RMA hits one of the fixed
    limits before the RMA limit.  This is relatively easy on POWER8 which
    has a 16GiB limit, harder on POWER9 which has a 1TiB limit.
  * Use a guest NUMA configuration which artificially constrains the RMA
    within the VRMA limit (the RMA must always fit within Node 0).

Previously, on KVM, we also temporarily reduced the rma_size to 256M so
that the we'd load the kernel and initrd safely, regardless of the VRMA
limit.  This was a) confusing, b) could significantly limit the size of
images we could load and c) introduced a behavioural difference between
KVM and TCG.  So we remove that as well.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Greg Kurz <groug@kaod.org>
2020-03-17 09:41:15 +11:00
..
e500-ccsr.h ppc: do not use ../ in include files 2013-03-01 13:57:33 +01:00
e500.c Merge tag 'patchew/20200219160953.13771-1-imammedo@redhat.com' of https://github.com/patchew-project/qemu into HEAD 2020-02-25 09:19:00 +01:00
e500.h platform-bus-device: use device plug callback instead of machine_done notifier 2018-05-10 18:10:56 +01:00
e500plat.c ppc/e500: use memdev for RAM 2020-02-19 16:50:00 +00:00
fdt.c target/ppc: Split page size information into a separate allocation 2018-04-27 18:05:22 +10:00
fw_cfg.c hw/ppc: Implement fw_cfg_arch_key_name() 2019-05-23 14:10:31 +02:00
Kconfig ppc/pnv: Fix PCI_EXPRESS dependency 2020-02-21 09:15:03 +11:00
mac_newworld.c ppc/mac_newworld: use memdev for RAM 2020-02-19 16:50:00 +00:00
mac_oldworld.c hw: Make MachineClass::is_default a boolean type 2020-02-28 14:57:19 -05:00
mac.h ide: Include hw/ide/internal a bit less outside hw/ide/ 2019-08-16 13:31:52 +02:00
Makefile.objs spapr: Add NVDIMM device support 2020-02-21 09:15:04 +11:00
mpc8544_guts.c sysemu: Split sysemu/runstate.h off sysemu/sysemu.h 2019-08-16 13:37:36 +02:00
mpc8544ds.c ppc/e500: use memdev for RAM 2020-02-19 16:50:00 +00:00
pnv_bmc.c ppc/pnv: Add a "pnor" const link property to the BMC internal simulator 2020-01-08 11:01:59 +11:00
pnv_core.c ppc/pnv: change the PowerNV machine devices to be non user creatable 2020-02-02 14:07:57 +11:00
pnv_homer.c ppc/pnv: change the PowerNV machine devices to be non user creatable 2020-02-02 14:07:57 +11:00
pnv_lpc.c hw/ppc/pnv: Fix typo in comment 2020-03-17 09:41:14 +11:00
pnv_occ.c ppc/pnv: change the PowerNV machine devices to be non user creatable 2020-02-02 14:07:57 +11:00
pnv_pnor.c ppc/pnv: improve error logging when a PNOR update fails 2020-02-02 14:07:57 +11:00
pnv_psi.c add device_legacy_reset function to prepare for reset api change 2020-01-30 16:02:03 +00:00
pnv_xscom.c ppc/pnv: Introduce PnvChipClass::xscom_pcba() method 2019-12-17 10:59:11 +11:00
pnv.c Merge tag 'patchew/20200219160953.13771-1-imammedo@redhat.com' of https://github.com/patchew-project/qemu into HEAD 2020-02-25 09:19:00 +01:00
ppc4xx_devs.c ppc/{ppc440_bamboo, sam460ex}: use memdev for RAM 2020-02-19 16:50:00 +00:00
ppc4xx_pci.c Include hw/hw.h exactly where needed 2019-08-16 13:31:52 +02:00
ppc405_boards.c ppc/ppc405_boards: use memdev for RAM 2020-02-19 16:50:00 +00:00
ppc405_uc.c Include hw/boards.h a bit less 2019-08-16 13:31:53 +02:00
ppc405.h ppc4xx: Export ECB and PLB emulation 2017-09-08 09:30:55 +10:00
ppc440_bamboo.c ppc/{ppc440_bamboo, sam460ex}: use memdev for RAM 2020-02-19 16:50:00 +00:00
ppc440_pcix.c Include hw/hw.h exactly where needed 2019-08-16 13:31:52 +02:00
ppc440_uc.c Let cpu_[physical]_memory() calls pass a boolean 'is_write' argument 2020-02-20 14:47:08 +01:00
ppc440.h ppc440_uc: Basic emulation of PPC440 DMA controller 2018-07-03 09:56:52 +10:00
ppc_booke.c sysemu: Split sysemu/runstate.h off sysemu/sysemu.h 2019-08-16 13:37:36 +02:00
ppc.c hw/ppc/prep: Remove the deprecated "prep" machine and the OpenHackware BIOS 2020-02-02 14:07:57 +11:00
ppce500_spin.c Clean up inclusion of sysemu/sysemu.h 2019-08-16 13:31:53 +02:00
prep_systemio.c qdev: set properties with device_class_set_props() 2020-01-24 20:59:15 +01:00
prep.c hw/ppc/prep: Remove the deprecated "prep" machine and the OpenHackware BIOS 2020-02-02 14:07:57 +11:00
rs6000_mc.c qdev: set properties with device_class_set_props() 2020-01-24 20:59:15 +01:00
sam460ex.c ppc/{ppc440_bamboo, sam460ex}: use memdev for RAM 2020-02-19 16:50:00 +00:00
spapr_caps.c ppc: spapr: Handle "ibm,nmi-register" and "ibm,nmi-interlock" RTAS calls 2020-02-03 11:33:11 +11:00
spapr_cpu_core.c spapr, ppc: Remove VPM0/RMLS hacks for POWER9 2020-03-17 09:41:15 +11:00
spapr_drc.c spapr: Fix handling of unplugged devices during CAS and migration 2020-02-21 09:15:04 +11:00
spapr_events.c spapr: Handle pending hot plug/unplug requests at CAS 2020-03-17 09:41:14 +11:00
spapr_hcall.c spapr: Don't attempt to clamp RMA to VRMA constraint 2020-03-17 09:41:15 +11:00
spapr_iommu.c vmstate: replace DeviceState with VMStateIf 2020-01-06 18:41:32 +04:00
spapr_irq.c spapr, pnv, xive: Add a "xive-fabric" link to the XIVE router 2020-01-08 11:01:59 +11:00
spapr_nvdimm.c spapr: Fix Coverity warning while validating nvdimm options 2020-03-17 09:41:14 +11:00
spapr_ovec.c spapr: Simplify ovec diff 2019-12-17 10:39:48 +11:00
spapr_pci_nvlink2.c error: Clean up unusual names of Error * variables 2019-12-18 08:36:15 +01:00
spapr_pci_vfio.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
spapr_pci.c add device_legacy_reset function to prepare for reset api change 2020-01-30 16:02:03 +00:00
spapr_rng.c qdev: set properties with device_class_set_props() 2020-01-24 20:59:15 +01:00
spapr_rtas_ddw.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
spapr_rtas.c spapr/rtas: Print message from "ibm,os-term" 2020-02-21 09:15:03 +11:00
spapr_rtc.c Include migration/vmstate.h less 2019-08-16 13:31:52 +02:00
spapr_tpm_proxy.c qdev: set properties with device_class_set_props() 2020-01-24 20:59:15 +01:00
spapr_vio.c spapr: Implement get_dt_compatible() callback 2020-02-02 14:07:57 +11:00
spapr.c spapr: Don't attempt to clamp RMA to VRMA constraint 2020-03-17 09:41:15 +11:00
trace-events spapr: Remove unhelpful tracepoints from spapr_irq_free_xics() 2019-10-04 19:08:22 +10:00
virtex_ml507.c Merge tag 'patchew/20200219160953.13771-1-imammedo@redhat.com' of https://github.com/patchew-project/qemu into HEAD 2020-02-25 09:19:00 +01:00