linux-kernel - Re: [PATCH v2 3/4] KVM: x86/mmu: explicitly check nx_hugepage in disallowed_hugepage

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Message-ID: <YkOH+k7sE2x5wz+f@google.com>
Date:   Tue, 29 Mar 2022 22:28:10 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Mingwei Zhang <mizhang@...gle.com>
Cc:     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>,
        David Matlack <dmatlack@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        Peter Xu <peterx@...hat.com>,
        Yosry Ahmed <yosryahmed@...gle.com>
Subject: Re: [PATCH v2 3/4] KVM: x86/mmu: explicitly check nx_hugepage in
 disallowed_hugepage_adjust()

On Tue, Mar 29, 2022, Sean Christopherson wrote:
> > Fixes: b8e8c8303ff2 ("kvm: mmu: ITLB_MULTIHIT mitigation")
> > Cc: stable@...r.kernel.org
> 
> I vote to keep the Fixes tag, but drop the Cc: stable@ and NAK any MANUALSEL/AUTOSEL
> for backporting this to stable trees.  Yes, it's a bug, but the NX huge page zapping
> kthread will (eventually) reclaim the lost performance.  On the flip side, if there's
> an edge case we mess up (see below), then we've introduced a far worse bug.

Doh, that's wrong.  The whole problem is that these pages aren't on the NX list...
I think I'd still vote to not send this to stable, but it's a weak vote.