linux-kernel - Re: [PATCH] KVM: x86/mmu: Stop zapping invalidated TDP MMU roots asynchronously

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Message-ID: <ZTLMcmj-ycWhZuTX@google.com>
Date:   Fri, 20 Oct 2023 11:52:34 -0700
From:   David Matlack <dmatlack@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     stable@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Pattara Teerapong <pteerapong@...gle.com>,
        David Stevens <stevensd@...gle.com>,
        Yiwei Zhang <zzyiwei@...gle.com>,
        Paul Hsia <paulhsia@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH] KVM: x86/mmu: Stop zapping invalidated TDP MMU roots
 asynchronously

On 2023-10-19 01:11 PM, Sean Christopherson wrote:
> [ Upstream commit 0df9dab891ff0d9b646d82e4fe038229e4c02451 ]
> 
> Stop zapping invalidate TDP MMU roots via work queue now that KVM
> preserves TDP MMU roots until they are explicitly invalidated.  Zapping
> roots asynchronously was effectively a workaround to avoid stalling a vCPU
> for an extended during if a vCPU unloaded a root, which at the time
> happened whenever the guest toggled CR0.WP (a frequent operation for some
> guest kernels).
> 
[...]
> 
> Reported-by: Pattara Teerapong <pteerapong@...gle.com>
> Cc: David Stevens <stevensd@...gle.com>
> Cc: Yiwei Zhang<zzyiwei@...gle.com>
> Cc: Paul Hsia <paulhsia@...gle.com>
> Cc: stable@...r.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> Message-Id: <20230916003916.2545000-4-seanjc@...gle.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> Cc: David Matlack <dmatlack@...gle.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---

Reviewed-by: David Matlack <dmatlack@...gle.com>
Tested-by: David Matlack <dmatlack@...gle.com>

(Ran all KVM selftests and kvm-unit-tests with lockdep enabled.)