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From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Ben Gardon <bgardon@google.com>,
	Makarand Sonare <makarandsonare@google.com>
Subject: Re: [PATCH 12/14] KVM: x86/mmu: Don't set dirty bits when disabling dirty logging w/ PML
Date: Thu, 18 Feb 2021 18:08:09 +0100	[thread overview]
Message-ID: <9293da48-8bad-0b70-4548-3df7931b6bee@redhat.com> (raw)
In-Reply-To: <20210213005015.1651772-13-seanjc@google.com>

On 13/02/21 01:50, Sean Christopherson wrote:
> This means that spurious PML entries will be created for memslots with 
> dirty logging disabled if at least one other memslot has dirty logging 
> enabled, but for all known use cases, dirty logging is a global VMM 
> control.

This is not true.  For example QEMU uses dirty logging to track changes 
to the framebuffer.

However, what you're saying below is true: after a MR_CREATE there will 
be no shadow pages, and when they are created with mmu_set_spte they 
will not have the dirty bits set.  So there's really no change here for 
the case of only some memslots having dirty logging enabled.  Queued 12 
and 13 as well then!

Paolo

> Furthermore, spurious PML entries are already possible since 
> dirty bits are set only when a dirty logging is turned off, i.e. 
> memslots that are never dirty logged will have dirty bits cleared.


  reply	other threads:[~2021-02-18 18:56 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-13  0:50 [PATCH 00/14] KVM: x86/mmu: Dirty logging fixes and improvements Sean Christopherson
2021-02-13  0:50 ` [PATCH 01/14] KVM: x86/mmu: Expand collapsible SPTE zap for TDP MMU to ZONE_DEVICE pages Sean Christopherson
2021-02-18 12:36   ` Paolo Bonzini
2021-02-13  0:50 ` [PATCH 02/14] KVM: x86/mmu: Don't unnecessarily write-protect small pages in TDP MMU Sean Christopherson
2021-02-13  0:50 ` [PATCH 03/14] KVM: x86/mmu: Split out max mapping level calculation to helper Sean Christopherson
2021-02-13  0:50 ` [PATCH 04/14] KVM: x86/mmu: Pass the memslot to the rmap callbacks Sean Christopherson
2021-02-13  0:50 ` [PATCH 05/14] KVM: x86/mmu: Consult max mapping level when zapping collapsible SPTEs Sean Christopherson
2021-02-18 12:43   ` Paolo Bonzini
2021-02-18 16:23     ` Sean Christopherson
2021-02-18 22:30       ` Mike Kravetz
2021-02-19  1:31         ` Sean Christopherson
2021-02-13  0:50 ` [PATCH 06/14] KVM: nVMX: Disable PML in hardware when running L2 Sean Christopherson
2021-02-13  0:50 ` [PATCH 07/14] KVM: x86/mmu: Expand on the comment in kvm_vcpu_ad_need_write_protect() Sean Christopherson
2021-02-13  0:50 ` [PATCH 08/14] KVM: x86/mmu: Make dirty log size hook (PML) a value, not a function Sean Christopherson
2021-02-18 12:45   ` Paolo Bonzini
2021-02-13  0:50 ` [PATCH 09/14] KVM: x86: Move MMU's PML logic to common code Sean Christopherson
2021-02-13  0:50 ` [PATCH 10/14] KVM: x86: Further clarify the logic and comments for toggling log dirty Sean Christopherson
2021-02-18 12:50   ` Paolo Bonzini
2021-02-18 16:15     ` Sean Christopherson
2021-02-18 16:56       ` Paolo Bonzini
2021-02-13  0:50 ` [PATCH 11/14] KVM: VMX: Dynamically enable/disable PML based on memslot dirty logging Sean Christopherson
2021-02-13  0:50 ` [PATCH 12/14] KVM: x86/mmu: Don't set dirty bits when disabling dirty logging w/ PML Sean Christopherson
2021-02-18 17:08   ` Paolo Bonzini [this message]
2021-02-13  0:50 ` [PATCH 13/14] KVM: x86: Fold "write-protect large" use case into generic write-protect Sean Christopherson
2021-02-13  0:50 ` [PATCH 14/14] KVM: x86/mmu: Remove a variety of unnecessary exports Sean Christopherson
2021-02-17 22:50 ` [PATCH 00/14] KVM: x86/mmu: Dirty logging fixes and improvements Sean Christopherson
2021-02-18 12:57 ` Paolo Bonzini

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