linux-kernel - Re: [PATCH 0/3] KVM: x86: Use "standard" mmu

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Date:   Mon, 5 Jun 2023 12:15:55 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jason Gunthorpe <jgg@...dia.com>,
        Alistair Popple <apopple@...dia.com>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 0/3] KVM: x86: Use "standard" mmu_notifier hook for APIC
 page

On 6/2/23 03:15, 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.
> 
> Sean Christopherson (3):
>    KVM: VMX: Retry APIC-access page reload if invalidation is in-progress
>    KVM: x86: Use standard mmu_notifier invalidate hooks for APIC access
>      page
>    KVM: x86/mmu: Trigger APIC-access page reload iff vendor code cares
> 
>   arch/x86/kvm/mmu/mmu.c   |  4 ++++
>   arch/x86/kvm/vmx/vmx.c   | 50 ++++++++++++++++++++++++++++++++++++----
>   arch/x86/kvm/x86.c       | 14 -----------
>   include/linux/kvm_host.h |  3 ---
>   virt/kvm/kvm_main.c      | 18 ---------------
>   5 files changed, 49 insertions(+), 40 deletions(-)
> 
> 
> base-commit: 39428f6ea9eace95011681628717062ff7f5eb5f


Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>

Paolo