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From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <seanjc@google.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Yosry Ahmed <yosryahmed@google.com>,
	Mingwei Zhang <mizhang@google.com>,
	Ben Gardon <bgardon@google.com>
Subject: Re: [PATCH v2 0/6] KVM: x86: Apply NX mitigation more precisely
Date: Fri, 29 Jul 2022 00:09:56 +0200	[thread overview]
Message-ID: <f8ccb892-cf79-62df-2752-2333467245cd@redhat.com> (raw)
In-Reply-To: <YuL9sB8ux88TJ9o0@google.com>

On 7/28/22 23:20, Sean Christopherson wrote:
> 
> Anyways, the bug we really care about is that by not precisely checking if a
> huge page is disallowed, KVM would refuse to create huge page after disabling
> dirty logging, which is a very noticeable performance issue for large VMs if
> a migration is canceled.  That particular bug has since been unintentionally
> fixed in the TDP MMU by zapping the non-leaf SPTE, but there are other paths
> that could similarly be affected, e.g. I believe zapping leaf SPTEs in response
> to a host page migration (mmu_notifier invalidation) to create a huge page would
> yield a similar result; KVM would see the shadow-present non-leaf SPTE and assume
> a huge page is disallowed.

Ok, thanks.  So this will be 5.21 material even during the -rc phase; I 
have posted a couple comments for patch 1 and 2.

One way to simplify the rmb/wmb logic could be to place the rmb/wmb 
respectively after loading iter.old_spte and in tdp_mmu_link_sp.  If you 
like it, feel free to integrate it in v3.

Paolo

  parent reply	other threads:[~2022-07-28 22:10 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-07-23  1:23 [PATCH v2 0/6] KVM: x86: Apply NX mitigation more precisely Sean Christopherson
2022-07-23  1:23 ` [PATCH v2 1/6] KVM: x86/mmu: Tag disallowed NX huge pages even if they're not tracked Sean Christopherson
2022-07-25 22:49   ` David Matlack
2022-07-25 23:26     ` Sean Christopherson
2022-07-25 23:45       ` David Matlack
2022-07-26  0:01         ` Sean Christopherson
2022-07-28 22:11   ` Paolo Bonzini
2022-07-23  1:23 ` [PATCH v2 2/6] KVM: x86/mmu: Properly account NX huge page workaround for nonpaging MMUs Sean Christopherson
2022-07-25 23:05   ` David Matlack
2022-07-25 23:08     ` David Matlack
2022-07-28 20:15   ` Paolo Bonzini
2022-07-23  1:23 ` [PATCH v2 3/6] KVM: x86/mmu: Set disallowed_nx_huge_page in TDP MMU before setting SPTE Sean Christopherson
2022-07-25 23:16   ` David Matlack
2022-07-23  1:23 ` [PATCH v2 4/6] KVM: x86/mmu: Track the number of TDP MMU pages, but not the actual pages Sean Christopherson
2022-07-25 23:21   ` David Matlack
2022-07-25 23:27     ` Sean Christopherson
2022-07-27  2:41   ` Yan Zhao
2022-07-27 19:04     ` Sean Christopherson
2022-07-29  1:02       ` Yan Zhao
2022-07-23  1:23 ` [PATCH v2 5/6] KVM: x86/mmu: Add helper to convert SPTE value to its shadow page Sean Christopherson
2022-07-25 23:23   ` David Matlack
2022-07-25 23:33     ` Sean Christopherson
2022-07-23  1:23 ` [PATCH v2 6/6] KVM: x86/mmu: explicitly check nx_hugepage in disallowed_hugepage_adjust() Sean Christopherson
2022-07-25 23:28   ` David Matlack
2022-07-26  5:37 ` [PATCH v2 0/6] KVM: x86: Apply NX mitigation more precisely Mingwei Zhang
2022-07-26 16:40   ` Sean Christopherson
2022-07-26 17:21     ` Sean Christopherson
2022-07-28 20:17 ` Paolo Bonzini
2022-07-28 21:20   ` Sean Christopherson
2022-07-28 21:41     ` Mingwei Zhang
2022-07-28 22:09     ` Paolo Bonzini [this message]
2022-07-28 22:15       ` Sean Christopherson

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