linux-kernel - Re: [PATCH v4 00/16] My AVIC patch queue

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Date:   Wed, 11 Aug 2021 10:06:43 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     Jim Mattson <jmattson@...gle.com>, linux-kernel@...r.kernel.org,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>, Joerg Roedel <joro@...tes.org>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>
Subject: Re: [PATCH v4 00/16] My AVIC patch queue

On 10/08/21 23:21, Maxim Levitsky wrote:
> On Tue, 2021-08-10 at 23:52 +0300, Maxim Levitsky wrote:
>> Hi!
>>
>> This is a series of bugfixes to the AVIC dynamic inhibition, which was
>> made while trying to fix bugs as much as possible in this area and trying
>> to make the AVIC+SYNIC conditional enablement work.
>>
>> * Patches 1,3-8 are code from Sean Christopherson which
> 
> I mean patches 1,4-8. I forgot about patch 3 which I also added,
> which just added a comment about parameters of the kvm_flush_remote_tlbs_with_address.
> 
> Best regards,
> 	Maxim Levitsky
> 
>>    implement an alternative approach of inhibiting AVIC without
>>    disabling its memslot.
>>
>>    V4: addressed review feedback.
>>
>> * Patch 2 is new and it fixes a bug in kvm_flush_remote_tlbs_with_address
>>
>> * Patches 9-10 in this series fix a race condition which can cause
>>    a lost write from a guest to APIC when the APIC write races
>>    the AVIC un-inhibition, and add a warning to catch this problem
>>    if it re-emerges again.
>>
>>    V4: applied review feedback from Paolo
>>
>> * Patch 11 is the patch from Vitaly about allowing AVIC with SYNC
>>    as long as the guest doesn’t use the AutoEOI feature. I only slightly
>>    changed it to expose the AutoEOI cpuid bit regardless of AVIC enablement.
>>
>>    V4: fixed a race that Paolo pointed out.
>>
>> * Patch 12 is a refactoring that is now possible in SVM AVIC inhibition code,
>>    because the RCU lock is not dropped anymore.
>>
>> * Patch 13-15 fixes another issue I found in AVIC inhibit code:
>>
>>    Currently avic_vcpu_load/avic_vcpu_put are called on userspace entry/exit
>>    from KVM (aka kvm_vcpu_get/kvm_vcpu_put), and these functions update the
>>    "is running" bit in the AVIC physical ID remap table and update the
>>    target vCPU in iommu code.
>>
>>    However both of these functions don't do anything when AVIC is inhibited
>>    thus the "is running" bit will be kept enabled during the exit to userspace.
>>    This shouldn't be a big issue as the caller
>>    doesn't use the AVIC when inhibited but still inconsistent and can trigger
>>    a warning about this in avic_vcpu_load.
>>
>>    To be on the safe side I think it makes sense to call
>>    avic_vcpu_put/avic_vcpu_load when inhibiting/uninhibiting the AVIC.
>>    This will ensure that the work these functions do is matched.
>>
>>    V4: I splitted a single patch to 3 patches to make it easier
>>        to review, and applied Paolo's review feedback.
>>
>> * Patch 16 removes the pointless APIC base
>>    relocation from AVIC to make it consistent with the rest of KVM.
>>
>>    (both AVIC and APICv only support default base, while regular KVM,
>>    sort of support any APIC base as long as it is not RAM.
>>    If guest attempts to relocate APIC base to non RAM area,
>>    while APICv/AVIC are active, the new base will be non accelerated,
>>    while the default base will continue to be AVIC/APICv backed).
>>
>>    On top of that if guest uses different APIC bases on different vCPUs,
>>    KVM doesn't honour the fact that the MMIO range should only be active
>>    on that vCPU.

No problem, b4 diff is my friend. :)  Queued, thanks.

Paolo