linux-kernel - Re: [PATCH 00/14] KVM: x86/mmu: Dirty logging fixes and improvements

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Date:   Wed, 17 Feb 2021 14:50:57 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ben Gardon <bgardon@...gle.com>,
        Makarand Sonare <makarandsonare@...gle.com>
Subject: Re: [PATCH 00/14] KVM: x86/mmu: Dirty logging fixes and improvements

On Fri, Feb 12, 2021, Sean Christopherson wrote:
> Paolo, this is more or less ready, but on final read-through before
> sending I realized it would be a good idea to WARN during VM destruction
> if cpu_dirty_logging_count is non-zero.  I wanted to get you this before
> the 5.12 window opens in case you want the TDP MMU fixes for 5.12.  I'll
> do the above change and retest next week (note, Monday is a US holiday).

Verified cpu_dirty_logging_count does indeed hit zero during VM destruction.

Adding a WARN to KVM would require adding an arch hook to kvm_free_memslots(),
otherwise the count will be non-zero if the VM is destroyed with dirty logging
active.  That doesn't seem worthwhile, so I'm not planning on pursuing a WARN
for the upstream code.