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Date:   Tue, 6 Jun 2023 13:43:32 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Sean Christopherson <seanjc@google.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, Alistair Popple <apopple@nvidia.com>,
        Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH 0/3] KVM: x86: Use "standard" mmu_notifier hook for APIC
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On Thu, Jun 01, 2023 at 06:15:15PM -0700, Sean Christopherson wrote:
> Convert VMX's handling of mmu_notifier invalidations of the APIC-access page
> from invalidate_range() to KVM's standard invalidate_range_{start,end}().
> 
> KVM (ab)uses invalidate_range() to fudge around not stalling vCPUs until
> relevant in-flight invalidations complete.  Abusing invalidate_range() works,
> but it requires one-off code in KVM, sets a bad precedent in KVM, and is
> blocking improvements to mmu_notifier's definition of invalidate_range()
> due to KVM's usage diverging wildly from the original intent of notifying
> IOMMUs of changes to shared page tables.
> 
> Clean up the mess by hooking x86's implementation of kvm_unmap_gfn_range()
> and stalling vCPUs by re-requesting KVM_REQ_APIC_PAGE_RELOAD until the
> invalidation completes.

I don't know much about kvm, but this looks like what I had in mind
and is a good way to use mmu notifiers

Thanks,
Jason