linux-kernel - Re: [PATCH 1/3] KVM: VMX: Retry APIC-access page reload if invalidation is in-progress

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Date:   Tue, 6 Jun 2023 14:39:11 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Alistair Popple <apopple@...dia.com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 1/3] KVM: VMX: Retry APIC-access page reload if
 invalidation is in-progress

On Tue, Jun 06, 2023 at 10:22:14AM -0700, Sean Christopherson wrote:
> On Tue, Jun 06, 2023, Alistair Popple wrote:
> > 
> > Thanks for doing this. I'm not overly familiar with KVM implementation
> > but am familiar with mmu notifiers so read through the KVM usage. Looks
> > like KVM is sort of doing something similar to what mmu_interval_notifiers
> > do and I wonder if some of that could be shared.
> 
> They're very, very similar.  At a glance, KVM likely could be moved over to the
> common interval tree implementation, but it would require a substantial amount of
> work in KVM, and various extensions to the mmu notifiers too.  I definitely wouldn't
> be opposed to converging KVM if someone wants to put in the effort, but at the same
> time I wouldn't recommend that anyone actually do the work as the ROI is likely
> very low.

I looked at it lightly a long time ago and came to sort of the same
conclusion, it might even be a negative for KVM as it isn't quite as
tightly inlined and lock free.

Jason