[PATCH v4 0/4] kvm/arm: New VMID allocator based on asid

[Shameer Kolothum]

Changes from v3:
- Main change is in patch #4, where the VMID is now set to an
  invalid one on vCPU schedule out. Introduced an 
  INVALID_ACTIVE_VMID which is basically a VMID 0 with generation 1.
  Since the basic allocator algorithm reserves vmid #0, it is never
  used as an active VMID. This (hopefully) will fix the issue of
  unnecessarily reserving VMID space with active_vmids when those
  VMs are no longer active[0] and at the same time address the
  problem noted in v3 wherein everything ends up in slow-path[1].

Testing:
 -Run with VMID bit set to 4 and maxcpus to 8 on D06. The test
  involves running concurrently 50 guests with 4 vCPUs. Each
  guest will then execute hackbench 5 times before exiting.
  No crash was observed for a 4-day continuous run.
  The latest branch is here,
   https://github.com/hisilicon/kernel-dev/tree/private-v5.16-rc1-vmid-v4

 -TLA+ model. Modified the asidalloc model to incorporate the new
  VMID algo. The main differences are,
  -flush_tlb_all() instead of local_tlb_flush_all() on rollover.
  -Introduced INVALID_VMID and vCPU Sched Out logic.
  -No CnP (Removed UniqueASIDAllCPUs & UniqueASIDActiveTask invariants).
  -Removed  UniqueVMIDPerCPU invariant for now as it looks like
   because of the speculative fetching with flush_tlb_all() there
   is a small window where this gets triggered. If I change the
   logic back to local_flush_tlb_all(), UniqueVMIDPerCPU seems to
   be fine. With my limited knowledge on TLA+ model, it is not
   clear to me whether this is a problem with the above logic
   or the VMID model implementation. Really appreciate any help
   with the model.
   The initial VMID TLA+ model is here,
   https://github.com/shamiali2008/kernel-tla/tree/private-vmidalloc-v1

Please take a look and let me know.

Thanks,
Shameer

[0] https://lore.kernel.org/kvmarm/20210721160614.GC11003@willie-the-truck/
[1] https://lore.kernel.org/kvmarm/20210803114034.GB30853@willie-the-truck/

History:
--------
v2 --> v3
  -Dropped adding a new static key and cpufeature for retrieving
   supported VMID bits. Instead, we now make use of the
   kvm_arm_vmid_bits variable (patch #2).

  -Since we expect less frequent rollover in the case of VMIDs,
   the TLB invalidation is now broadcasted on rollover instead
   of keeping per CPU flush_pending info and issuing a local
   context flush.

  -Clear active_vmids on vCPU schedule out to avoid unnecessarily
   reserving the VMID space(patch #3).

  -I have kept the struct kvm_vmid as it is for now(instead of a
   typedef as suggested), as we may soon add another variable to
   it when we introduce Pinned KVM VMID support.

RFCv1 --> v2
   -Dropped "pinned VMID" support for now.
   -Dropped RFC tag.
RFCv1
   https://lore.kernel.org/kvmarm/20210506165232.1969-1-shameerali.kolothum.thodi@xxxxxxxxxx/

Julien Grall (1):
  KVM: arm64: Align the VMID allocation with the arm64 ASID

Shameer Kolothum (3):
  KVM: arm64: Introduce a new VMID allocator for KVM
  KVM: arm64: Make VMID bits accessible outside of allocator
  KVM: arm64: Make active_vmids invalid on vCPU schedule out

 arch/arm64/include/asm/kvm_host.h     |  10 +-
 arch/arm64/include/asm/kvm_mmu.h      |   4 +-
 arch/arm64/kernel/image-vars.h        |   3 +
 arch/arm64/kvm/Makefile               |   2 +-
 arch/arm64/kvm/arm.c                  | 106 +++-----------
 arch/arm64/kvm/hyp/nvhe/mem_protect.c |   3 +-
 arch/arm64/kvm/mmu.c                  |   1 -
 arch/arm64/kvm/vmid.c                 | 196 ++++++++++++++++++++++++++
 8 files changed, 228 insertions(+), 97 deletions(-)
 create mode 100644 arch/arm64/kvm/vmid.c

-- 
2.17.1