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* [PATCH v4 0/7] Lazily allocate memslot rmaps
@ 2021-05-11 17:16 Ben Gardon
  2021-05-11 17:16 ` [PATCH v4 1/7] KVM: x86/mmu: Deduplicate rmap freeing Ben Gardon
                   ` (6 more replies)
  0 siblings, 7 replies; 19+ messages in thread
From: Ben Gardon @ 2021-05-11 17:16 UTC (permalink / raw)
  To: linux-kernel, kvm
  Cc: Paolo Bonzini, Peter Xu, Sean Christopherson, Peter Shier,
	Yulei Zhang, Wanpeng Li, Xiao Guangrong, Kai Huang, Keqian Zhu,
	David Hildenbrand, Ben Gardon

This series enables KVM to save memory when using the TDP MMU by waiting
to allocate memslot rmaps until they are needed. To do this, KVM tracks
whether or not a shadow root has been allocated. In order to get away
with not allocating the rmaps, KVM must also be sure to skip operations
which iterate over the rmaps. If the TDP MMU is in use and we have not
allocated a shadow root, these operations would essentially be op-ops
anyway. Skipping the rmap operations has a secondary benefit of avoiding
acquiring the MMU lock in write mode in many cases, substantially
reducing MMU lock contention.

This series was tested on an Intel Skylake machine. With the TDP MMU off
and on, this introduced no new failures on kvm-unit-tests or KVM selftests.

Changelog:
v2:
	Incorporated feedback from Paolo and Sean
	Replaced the memslot_assignment_lock with slots_arch_lock, which
	has a larger critical section.

v3:
	Removed shadow_mmu_active as suggested by Sean
	Removed everything except adding a return value to
	kvm_mmu_init_tdp_mmu from patch 1 of v2
	Added RCU protection and better memory ordering for installing the
	memslot rmaps as suggested by Paolo
	Reordered most of the patches

v4:
	Renamed functions to allocate and free memslots based on feedback
	from David.
	Eliminated the goto in memslot_rmap_alloc, as David suggested.
	Eliminated kvm_memslots_have_rmaps and updated comments on uses of
	memslots_have_rmaps. Suggested by Paolo.
	Changed the description on patch 7 to one Paolo suggested.
	Collected Reviewed-by tags from David.
	Dropped the patch to add RCU notations to rmap accesses.

Ben Gardon (7):
  KVM: x86/mmu: Deduplicate rmap freeing
  KVM: x86/mmu: Factor out allocating memslot rmap
  KVM: mmu: Refactor memslot copy
  KVM: mmu: Add slots_arch_lock for memslot arch fields
  KVM: x86/mmu: Add a field to control memslot rmap allocation
  KVM: x86/mmu: Skip rmap operations if rmaps not allocated
  KVM: x86/mmu: Lazily allocate memslot rmaps

 arch/x86/include/asm/kvm_host.h |   8 ++
 arch/x86/kvm/mmu/mmu.c          | 153 +++++++++++++++++++++-----------
 arch/x86/kvm/mmu/tdp_mmu.c      |   6 +-
 arch/x86/kvm/mmu/tdp_mmu.h      |   4 +-
 arch/x86/kvm/x86.c              | 108 ++++++++++++++++++----
 include/linux/kvm_host.h        |   9 ++
 virt/kvm/kvm_main.c             |  54 ++++++++---
 7 files changed, 255 insertions(+), 87 deletions(-)

-- 
2.31.1.607.g51e8a6a459-goog


^ permalink raw reply	[flat|nested] 19+ messages in thread

end of thread, other threads:[~2021-05-11 20:04 UTC | newest]

Thread overview: 19+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-05-11 17:16 [PATCH v4 0/7] Lazily allocate memslot rmaps Ben Gardon
2021-05-11 17:16 ` [PATCH v4 1/7] KVM: x86/mmu: Deduplicate rmap freeing Ben Gardon
2021-05-11 17:16 ` [PATCH v4 2/7] KVM: x86/mmu: Factor out allocating memslot rmap Ben Gardon
2021-05-11 17:56   ` Sean Christopherson
2021-05-11 18:17     ` Ben Gardon
2021-05-11 18:56       ` David Hildenbrand
2021-05-11 17:16 ` [PATCH v4 3/7] KVM: mmu: Refactor memslot copy Ben Gardon
2021-05-11 18:47   ` Sean Christopherson
2021-05-11 17:16 ` [PATCH v4 4/7] KVM: mmu: Add slots_arch_lock for memslot arch fields Ben Gardon
2021-05-11 18:55   ` Sean Christopherson
2021-05-11 19:21   ` Sean Christopherson
2021-05-11 19:29     ` Paolo Bonzini
2021-05-11 17:16 ` [PATCH v4 5/7] KVM: x86/mmu: Add a field to control memslot rmap allocation Ben Gardon
2021-05-11 17:16 ` [PATCH v4 6/7] KVM: x86/mmu: Skip rmap operations if rmaps not allocated Ben Gardon
2021-05-11 19:51   ` Sean Christopherson
2021-05-11 17:16 ` [PATCH v4 7/7] KVM: x86/mmu: Lazily allocate memslot rmaps Ben Gardon
2021-05-11 18:57   ` Sean Christopherson
2021-05-11 20:03   ` Sean Christopherson
2021-05-11 20:04     ` Sean Christopherson

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