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[v3,0/5] Migrate non-migrated pages of a SVM.

Message ID 1594458827-31866-1-git-send-email-linuxram@us.ibm.com (mailing list archive)
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Series Migrate non-migrated pages of a SVM. | expand

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Ram Pai July 11, 2020, 9:13 a.m. UTC 
The time taken to switch a VM to Secure-VM, increases by the size of the VM.  A
100GB VM takes about 7minutes. This is unacceptable.  This linear increase is
caused by a suboptimal behavior by the Ultravisor and the Hypervisor.  The
Ultravisor unnecessarily migrates all the GFN of the VM from normal-memory to
secure-memory. It has to just migrate the necessary and sufficient GFNs.

However when the optimization is incorporated in the Ultravisor, the Hypervisor
starts misbehaving. The Hypervisor has a inbuilt assumption that the Ultravisor
will explicitly request to migrate, each and every GFN of the VM. If only
necessary and sufficient GFNs are requested for migration, the Hypervisor
continues to manage the remaining GFNs as normal GFNs. This leads of memory
corruption, manifested consistently when the SVM reboots.

The same is true, when a memory slot is hotplugged into a SVM. The Hypervisor
expects the ultravisor to request migration of all GFNs to secure-GFN.  But the
hypervisor cannot handle any H_SVM_PAGE_IN requests from the Ultravisor, done
in the context of UV_REGISTER_MEM_SLOT ucall.  This problem manifests as random
errors in the SVM, when a memory-slot is hotplugged.

This patch series automatically migrates the non-migrated pages of a SVM,
     and thus solves the problem.

Testing: Passed rigorous testing using various sized SVMs.

Changelog:

v3: . Optimized the page-migration retry-logic. 
    . Relax and relinquish the cpu regularly while bulk migrating
    	the non-migrated pages. This issue was causing soft-lockups.
	Fixed it.
    . Added a new patch, to retry page-migration a couple of times
    	before returning H_BUSY in H_SVM_PAGE_IN. This issue was
	seen a few times in a 24hour continuous reboot test of the SVMs.

v2: . fixed a bug observed by Laurent. The state of the GFN's associated
	with Secure-VMs were not reset during memslot flush.
    . Re-organized the code, for easier review.
    . Better description of the patch series.

v1: fixed a bug observed by Bharata. Pages that where paged-in and later
paged-out must also be skipped from migration during H_SVM_INIT_DONE.

Laurent Dufour (1):
  KVM: PPC: Book3S HV: migrate hot plugged memory

Ram Pai (4):
  KVM: PPC: Book3S HV: Disable page merging in H_SVM_INIT_START
  KVM: PPC: Book3S HV: track the state GFNs associated with secure VMs
  KVM: PPC: Book3S HV: migrate remaining normal-GFNs to secure-GFNs in
    H_SVM_INIT_DONE
  KVM: PPC: Book3S HV: retry page migration before erroring-out
    H_SVM_PAGE_IN

 Documentation/powerpc/ultravisor.rst        |   3 +
 arch/powerpc/include/asm/kvm_book3s_uvmem.h |   2 +
 arch/powerpc/kvm/book3s_hv.c                |  10 +-
 arch/powerpc/kvm/book3s_hv_uvmem.c          | 487 ++++++++++++++++++++++++----
 4 files changed, 429 insertions(+), 73 deletions(-)