------- Comment From leona...@ibm.com 2019-03-14 15:47 EDT-------
Patchset SRU

* VMs have a high chance to hit guest migration issues if more than one guest 
migration happens at a time, while using THP on ppc64le.

* Migrating VMs in parallel will cause at least one guest to crash about
half the time.  Since VM migration is a upgrade/uptime strategy this has
a fairly large customer impact.

* The uploaded patches correct the behavior of THP on guests. They are
available on v4.18.x onwards.

[Test Case]

* One can reproduce the bug by trying two guest migrations, at the same
time, following this instructions on comment 12:

[Regression Potential]

* These patches are already on linux-stable since v4.18.15 (also on
hwe), so there is low regression chance.

8afc7da95a7e [Bionic] KVM: PPC: Book3S HV: Avoid crash from THP collapse during 
radix page fault
82f7758a9c99 [Bionic] KVM: PPC: Book3S HV: Don't use compound_order to 
determine host mapping size
b0f7664dc993 [Bionic] KVM: PPC: Book3S HV: Use correct pagesize in 
1991612ab005 [Bionic] KVM: PPC: Book3S HV: radix: Do not clear partition PTE 
when RC or write bits do not match
04fea11aa5fe [Bionic] KVM: PPC: Book3S HV: radix: Refine IO region partition 
scope attributes
9037e89d8093 [Bionic] KVM: PPC: Book3S HV: Make radix handle process scoped 
LPID flush in C, with relocation on
ed0a86a433c7 [Bionic] KVM: PPC: Book3S HV: Make radix use the Linux translation 
flush functions for partition scope
0effe5dc3cf4 [Bionic] KVM: PPC: Book3S HV: Recursively unmap all page table 
entries when unmapping
42cbaef5361b [Bionic] KVM: PPC: Book3S HV: Use a helper to unmap ptes in the 
radix fault path
414207e08540 [Bionic] powerpc/mm/radix: implement LPID based TLB flushes to be 
used by KVM
eb2a70df7099 [Bionic] powerpc/mm/radix: Remove unused code
ad052e60a417 [Bionic] powerpc/kvm: Switch kvm pmd allocator to custom allocator
bb2c03e387f4 [Bionic] KVM: PPC: Book 3S HV: Do ptesync in radix guest exit path
699642e0a4f8 [Bionic] KVM: PPC: Book3S HV: Make radix clear pte when unmapping
297755f60b17 [Bionic] KVM: PPC: Book3S HV: Make radix use correct tlbie 
sequence in kvmppc_radix_tlbie_page
d5f5570b7df4 [Bionic] KVM: PPC: Book3S HV: Use __gfn_to_pfn_memslot() in page 
fault handler
b0adb3223100 [Bionic] KVM: PPC: Book3S HV: Handle 1GB pages in radix page fault 
5be468e7408b [Bionic] KVM: PPC: Book3S HV: Streamline setting of reference and 
change bits
860816ea1680 [Bionic] KVM: PPC: Book3S HV: Radix page fault handler 
7fe24f427a09 [Bionic] KVM: PPC: Remove unused kvm_unmap_hva callback

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  Avoid migration issues with aligned 2MB THB

Status in The Ubuntu-power-systems project:
Status in linux package in Ubuntu:
Status in qemu package in Ubuntu:
Status in linux source package in Bionic:
Status in linux source package in Cosmic:

Bug description:
  FYI: This blocks bug 1781526 - once this one here is resolved we can
  go on with SRU considerations for 1781526

  ------- Comment From jhop...@us.ibm.com 2018-08-20 17:12 EDT-------

  Hi, in some environments it was observed that this qemu patch to
  enable THP made it more likely to hit guest migration issues, however
  the following kernel patch resolves those migration issues:

  KVM: PPC: Book3S HV: Use correct pagesize in kvm_unmap_radix()

  Once merged upstream, it would be good to include that change as well
  to avoid potential migration problems. Should I open a new bug for
  that or is it better to track here?

  Note Paelzer: I have not seen related migration issues myself, but it
  seems reasonable and confirmed by IBM.

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