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From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>,
	Janosch Frank <frankja@linux.ibm.com>,
	Claudio Imbrenda <imbrenda@linux.ibm.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	David Hildenbrand <david@redhat.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	David Matlack <dmatlack@google.com>,
	Ben Gardon <bgardon@google.com>,
	Mingwei Zhang <mizhang@google.com>
Subject: Re: [PATCH v3 22/28] KVM: x86/mmu: Zap defunct roots via asynchronous worker
Date: Wed, 2 Mar 2022 19:33:53 +0000	[thread overview]
Message-ID: <Yh/GoUPxMRyFqFc5@google.com> (raw)
In-Reply-To: <f4189f26-eff9-9fd0-40a1-69ac7759dedf@redhat.com>

On Wed, Mar 02, 2022, Paolo Bonzini wrote:
> On 3/2/22 19:01, Sean Christopherson wrote:
> > > It passes a smoke test, and also resolves the debate on the fate of patch 1.
> > +1000, I love this approach.  Do you want me to work on a v3, or shall I let you
> > have the honors?
> 
> I'm already running the usual battery of tests, so I should be able to post
> it either tomorrow (early in my evening) or Friday morning.

Gah, now I remember why I didn't use an async worker.  kvm_mmu_zap_all_fast()
must ensure all SPTEs are zapped and their dirty/accessed data written back to
the primary MMU prior to returning.  Once the memslot update completes, the old
deleted/moved memslot is no longer reachable by the mmu_notifier.  If an mmu_notifier
zaps pfns reachable via the root, KVM will do nothing because there's no relevant
memslot.

So we can use workers, but kvm_mmu_zap_all_fast() would need to flush all workers
before returning, which ends up being no different than putting the invalid roots
on a different list.

What about that idea?  Put roots invalidated by "fast zap" on _another_ list?
My very original idea of moving the roots to a separate list didn't work because
the roots needed to be reachable by the mmu_notifier.  But we could just add
another list_head (inside the unsync_child_bitmap union) and add the roots to
_that_ list.

Let me go resurrect that patch from v1 and tweak it to keep the roots on the old
list, but add them to a new list as well.  That would get rid of the invalid
root iterator stuff.

  reply	other threads:[~2022-03-02 19:34 UTC|newest]

Thread overview: 79+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-26  0:15 [PATCH v3 00/28] KVM: x86/mmu: Overhaul TDP MMU zapping and flushing Sean Christopherson
2022-02-26  0:15 ` [PATCH v3 01/28] KVM: x86/mmu: Use common iterator for walking invalid TDP MMU roots Sean Christopherson
2022-03-02 19:08   ` Mingwei Zhang
2022-03-02 19:51     ` Sean Christopherson
2022-03-03  0:57       ` Mingwei Zhang
2022-02-26  0:15 ` [PATCH v3 02/28] KVM: x86/mmu: Check for present SPTE when clearing dirty bit in TDP MMU Sean Christopherson
2022-03-02 19:50   ` Mingwei Zhang
2022-02-26  0:15 ` [PATCH v3 03/28] KVM: x86/mmu: Fix wrong/misleading comments in TDP MMU fast zap Sean Christopherson
2022-02-28 23:15   ` Ben Gardon
2022-02-26  0:15 ` [PATCH v3 04/28] KVM: x86/mmu: Formalize TDP MMU's (unintended?) deferred TLB flush logic Sean Christopherson
2022-03-02 23:59   ` Mingwei Zhang
2022-03-03  0:12     ` Sean Christopherson
2022-03-03  1:20       ` Mingwei Zhang
2022-03-03  1:41         ` Sean Christopherson
2022-03-03  4:50           ` Mingwei Zhang
2022-03-03 16:45             ` Sean Christopherson
2022-02-26  0:15 ` [PATCH v3 05/28] KVM: x86/mmu: Document that zapping invalidated roots doesn't need to flush Sean Christopherson
2022-02-28 23:17   ` Ben Gardon
2022-02-26  0:15 ` [PATCH v3 06/28] KVM: x86/mmu: Require mmu_lock be held for write in unyielding root iter Sean Christopherson
2022-02-28 23:26   ` Ben Gardon
2022-02-26  0:15 ` [PATCH v3 07/28] KVM: x86/mmu: Check for !leaf=>leaf, not PFN change, in TDP MMU SP removal Sean Christopherson
2022-03-01  0:11   ` Ben Gardon
2022-03-03 18:02   ` Mingwei Zhang
2022-02-26  0:15 ` [PATCH v3 08/28] KVM: x86/mmu: Batch TLB flushes from TDP MMU for MMU notifier change_spte Sean Christopherson
2022-03-03 18:08   ` Mingwei Zhang
2022-02-26  0:15 ` [PATCH v3 09/28] KVM: x86/mmu: Drop RCU after processing each root in MMU notifier hooks Sean Christopherson
2022-03-03 18:24   ` Mingwei Zhang
2022-03-03 18:32   ` Mingwei Zhang
2022-02-26  0:15 ` [PATCH v3 10/28] KVM: x86/mmu: Add helpers to read/write TDP MMU SPTEs and document RCU Sean Christopherson
2022-03-03 18:34   ` Mingwei Zhang
2022-02-26  0:15 ` [PATCH v3 11/28] KVM: x86/mmu: WARN if old _or_ new SPTE is REMOVED in non-atomic path Sean Christopherson
2022-03-03 18:37   ` Mingwei Zhang
2022-02-26  0:15 ` [PATCH v3 12/28] KVM: x86/mmu: Refactor low-level TDP MMU set SPTE helper to take raw vals Sean Christopherson
2022-03-03 18:47   ` Mingwei Zhang
2022-02-26  0:15 ` [PATCH v3 13/28] KVM: x86/mmu: Zap only the target TDP MMU shadow page in NX recovery Sean Christopherson
2022-02-26  0:15 ` [PATCH v3 14/28] KVM: x86/mmu: Skip remote TLB flush when zapping all of TDP MMU Sean Christopherson
2022-03-01  0:19   ` Ben Gardon
2022-03-03 18:50   ` Mingwei Zhang
2022-02-26  0:15 ` [PATCH v3 15/28] KVM: x86/mmu: Add dedicated helper to zap TDP MMU root shadow page Sean Christopherson
2022-03-01  0:32   ` Ben Gardon
2022-03-03 21:19   ` Mingwei Zhang
2022-03-03 21:24     ` Mingwei Zhang
2022-03-03 23:06       ` Sean Christopherson
2022-02-26  0:15 ` [PATCH v3 16/28] KVM: x86/mmu: Require mmu_lock be held for write to zap TDP MMU range Sean Christopherson
2022-02-26  0:15 ` [PATCH v3 17/28] KVM: x86/mmu: Zap only TDP MMU leafs in kvm_zap_gfn_range() Sean Christopherson
2022-02-26  0:15 ` [PATCH v3 18/28] KVM: x86/mmu: Do remote TLB flush before dropping RCU in TDP MMU resched Sean Christopherson
2022-02-26  0:15 ` [PATCH v3 19/28] KVM: x86/mmu: Defer TLB flush to caller when freeing TDP MMU shadow pages Sean Christopherson
2022-02-26  0:15 ` [PATCH v3 20/28] KVM: x86/mmu: Allow yielding when zapping GFNs for defunct TDP MMU root Sean Christopherson
2022-03-01 18:21   ` Paolo Bonzini
2022-03-01 19:43     ` Sean Christopherson
2022-03-01 20:12       ` Paolo Bonzini
2022-03-02  2:13         ` Sean Christopherson
2022-03-02 14:54           ` Paolo Bonzini
2022-03-02 17:43             ` Sean Christopherson
2022-02-26  0:15 ` [PATCH v3 21/28] KVM: x86/mmu: Zap roots in two passes to avoid inducing RCU stalls Sean Christopherson
2022-03-01  0:43   ` Ben Gardon
2022-02-26  0:15 ` [PATCH v3 22/28] KVM: x86/mmu: Zap defunct roots via asynchronous worker Sean Christopherson
2022-03-01 17:57   ` Ben Gardon
2022-03-02 17:25   ` Paolo Bonzini
2022-03-02 17:35     ` Sean Christopherson
2022-03-02 18:33       ` David Matlack
2022-03-02 18:36         ` Paolo Bonzini
2022-03-02 18:01     ` Sean Christopherson
2022-03-02 18:20       ` Paolo Bonzini
2022-03-02 19:33         ` Sean Christopherson [this message]
2022-03-02 20:14           ` Paolo Bonzini
2022-03-02 20:47             ` Sean Christopherson
2022-03-02 21:22               ` Paolo Bonzini
2022-03-02 22:25                 ` Sean Christopherson
2022-02-26  0:15 ` [PATCH v3 23/28] KVM: x86/mmu: Check for a REMOVED leaf SPTE before making the SPTE Sean Christopherson
2022-03-01 18:06   ` Ben Gardon
2022-02-26  0:15 ` [PATCH v3 24/28] KVM: x86/mmu: WARN on any attempt to atomically update REMOVED SPTE Sean Christopherson
2022-02-26  0:15 ` [PATCH v3 25/28] KVM: selftests: Move raw KVM_SET_USER_MEMORY_REGION helper to utils Sean Christopherson
2022-02-26  0:15 ` [PATCH v3 26/28] KVM: selftests: Split out helper to allocate guest mem via memfd Sean Christopherson
2022-02-28 23:36   ` David Woodhouse
2022-03-02 18:36     ` Paolo Bonzini
2022-03-02 21:55       ` David Woodhouse
2022-02-26  0:15 ` [PATCH v3 27/28] KVM: selftests: Define cpu_relax() helpers for s390 and x86 Sean Christopherson
2022-02-26  0:15 ` [PATCH v3 28/28] KVM: selftests: Add test to populate a VM with the max possible guest mem Sean Christopherson

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