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Reply-To: Sean Christopherson <seanjc@google.com>
Date:   Fri, 15 Sep 2023 17:39:13 -0700
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Message-ID: <20230916003916.2545000-1-seanjc@google.com>
Subject: [PATCH 0/3] KVM: x86/mmu: Drop async zapping of TDP MMU roots
From:   Sean Christopherson <seanjc@google.com>
To:     Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        Pattara Teerapong <pteerapong@google.com>,
        David Stevens <stevensd@google.com>,
        Yiwei Zhang <zzyiwei@google.com>,
        Paul Hsia <paulhsia@google.com>
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Precedence: bulk

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
-- 
2.42.0.459.ge4e396fd5e-goog