mbox series

[0/3] KVM: x86/mmu: Drop async zapping of TDP MMU roots

Message ID 20230916003916.2545000-1-seanjc@google.com
Headers
Series KVM: x86/mmu: Drop async zapping of TDP MMU roots |

Message

Sean Christopherson Sept. 16, 2023, 12:39 a.m. UTC 
  Yank out the asynchronous zapping of TDP MMU roots.  In some setups, using
unbounded workqueues can consumes all CPUs for extended durations, and
create significant jitter in the system.

Specifically, the behavior causes audio glitches in ChromeOS VMs with
virtio-gpu when running games in the guest.  Gory details in patch 3.

I tagged all of this for stable so that this gets back to v6.1 (I already
did the backport to verify it's not awful).  This bug is bad enough that
the workaround for the ChromeOS usecase is to simply disable the TDP MMU,
which I really do not want to do for the v6.1 kernel (or the v6.6. kernel).

Sean Christopherson (3):
  KVM: x86/mmu: Open code walking TDP MMU roots for mmu_notifier's zap
    SPTEs
  KVM: x86/mmu: Take "shared" instead of "as_id" TDP MMU's yield-safe
    iterator
  KVM: x86/mmu: Stop zapping invalidated TDP MMU roots asynchronously

 arch/x86/include/asm/kvm_host.h |   3 +-
 arch/x86/kvm/mmu/mmu.c          |  21 ++---
 arch/x86/kvm/mmu/mmu_internal.h |  13 ++-
 arch/x86/kvm/mmu/tdp_mmu.c      | 147 ++++++++++++++------------------
 arch/x86/kvm/mmu/tdp_mmu.h      |   5 +-
 arch/x86/kvm/x86.c              |   5 +-
 6 files changed, 80 insertions(+), 114 deletions(-)


base-commit: 0bb80ecc33a8fb5a682236443c1e740d5c917d1d

Comments

Paolo Bonzini Sept. 22, 2023, 8:40 p.m. UTC | #1 
Queued, thanks.

I changed a bit the splitting of the patches, to avoid mixing removal
of one argument and with the addition of another (splitting into four
patches wasn't particularly enlightening for a couple lines change),
but checked that the final result is the same.

Paolo