[v4] s390: stop abusing memory_region_allocate_system_memory()

[Qemu-devel] [PATCH for-4.2 v4 0/2] s390: stop abusing memory_region_allocate_system_memory()

Igor Mammedov posted 2 patches 4 years, 8 months ago

Diff against v1 v2 v3 v6 v7
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Test asan passed

Test FreeBSD passed

Test checkpatch passed

Test docker-mingw@fedora passed

Test docker-clang@ubuntu passed

Test s390x passed

Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/qemu tags/patchew/20190806094834.7691-1-imammedo@redhat.com

Maintainers: Paolo Bonzini <pbonzini@redhat.com>, Richard Henderson <rth@twiddle.net>, Cornelia Huck <cohuck@redhat.com>, Halil Pasic <pasic@linux.ibm.com>, David Hildenbrand <david@redhat.com>, Christian Borntraeger <borntraeger@de.ibm.com>

There is a newer version of this series

include/sysemu/kvm_int.h   |  1 +
accel/kvm/kvm-all.c        | 80 +++++++++++++++++++++++---------------
hw/s390x/s390-virtio-ccw.c | 30 ++------------
target/s390x/kvm.c         | 12 ++++++
4 files changed, 65 insertions(+), 58 deletions(-)

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[Qemu-devel] [PATCH for-4.2 v4 0/2] s390: stop abusing memory_region_allocate_system_memory()

Posted by Igor Mammedov 4 years, 8 months ago

Changelog:
  since v3:
    - fix compilation issue
    - advance HVA along with GPA in kvm_set_phys_mem()
  since v2:
    - break migration from old QEMU (since 2.12-4.1) for guest with >8TB RAM
      and drop migratable aliases patch as was agreed during v2 review
    - drop 4.2 machines patch as it's not prerequisite anymore
  since v1:
    - include 4.2 machines patch for adding compat RAM layout on top
    - 2/4 add missing in v1 patch for splitting too big MemorySection on
          several memslots
    - 3/4 amend code path on alias destruction to ensure that RAMBlock is
          cleaned properly
    - 4/4 add compat machine code to keep old layout (migration-wise) for
          4.1 and older machines 


While looking into unifying guest RAM allocation to use hostmem backends
for initial RAM (especially when -mempath is used) and retiring
memory_region_allocate_system_memory() API, leaving only single hostmem backend,
I was inspecting how currently it is used by boards and it turns out several
boards abuse it by calling the function several times (despite documented contract
forbiding it).

s390 is one of such boards where KVM limitation on memslot size got propagated
to board design and memory_region_allocate_system_memory() was abused to satisfy
KVM requirement for max RAM chunk where memory region alias would suffice.

Unfortunately, memory_region_allocate_system_memory() usage created migration
dependency where guest RAM is transferred in migration stream as several RAMBlocks
if it's more than KVM_SLOT_MAX_BYTES. During v2 review it was agreed to ignore
migration breakage (documenting it in release notes) and leaving only KVM fix.

In order to replace these several RAM chunks with a single memdev and keep it
working with KVM memslot size limit, following was done:
   * [1/2] split too big RAM chunk inside of KVM code on several memory slots
           if necessary
   * [2/2] drop manual ram splitting in s390 code


CC: pbonzini@redhat.com
CC: qemu-s390x@nongnu.org
CC: borntraeger@de.ibm.com
CC: thuth@redhat.com
CC: david@redhat.com
CC: cohuck@redhat.com




Igor Mammedov (2):
  kvm: s390: split too big memory section on several memslots
  s390: do not call memory_region_allocate_system_memory() multiple
    times

 include/sysemu/kvm_int.h   |  1 +
 accel/kvm/kvm-all.c        | 80 +++++++++++++++++++++++---------------
 hw/s390x/s390-virtio-ccw.c | 30 ++------------
 target/s390x/kvm.c         | 12 ++++++
 4 files changed, 65 insertions(+), 58 deletions(-)

-- 
2.18.1