From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Maxim Levitsky <mlevitsk@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 0/4] KVM: x86: APICv cleanups
Date: Mon, 25 Oct 2021 15:59:40 +0000 [thread overview]
Message-ID: <YXbUbB+l++P3XSZ5@google.com> (raw)
In-Reply-To: <674bc620-f013-d826-a4d4-00a142755a9e@redhat.com>
On Mon, Oct 25, 2021, Paolo Bonzini wrote:
> On 25/10/21 16:35, Sean Christopherson wrote:
> > > So yeah, I think you're right.
> > Yep. The alternative would be to explicitly check for a pending APICv update.
> > I don't have a strong opinion, I dislike both options equally:-)
>
> No, checking for the update is worse and with this example, I can now point
> my finger on why I preferred the VM check even before: because even though
> the page fault path runs in vCPU context and uses a vCPU-specific role,
> overall the page tables are still per-VM.
Arguably the lack of incorporation into the page role is the underlying bug, and
all the shenanigans with synchronizing updates are just workarounds for that bug.
I.e. page tables are never strictly per-VM, they're per-role, but we fudge it in
this case because we don't want to take on the overhead of maintaining two sets
of page tables to handle APICv.
next prev parent reply other threads:[~2021-10-25 15:59 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-22 0:49 [PATCH v2 0/4] KVM: x86: APICv cleanups Sean Christopherson
2021-10-22 0:49 ` [PATCH v2 1/4] KVM: x86/mmu: Use vCPU's APICv status when handling APIC_ACCESS memslot Sean Christopherson
2021-10-22 0:49 ` [PATCH v2 2/4] KVM: x86: Move SVM's APICv sanity check to common x86 Sean Christopherson
2021-10-22 0:49 ` [PATCH v2 3/4] KVM: x86: Move apicv_active flag from vCPU to in-kernel local APIC Sean Christopherson
2021-10-22 0:49 ` [PATCH v2 4/4] KVM: x86: Use rw_semaphore for APICv lock to allow vCPU parallelism Sean Christopherson
2021-10-22 10:12 ` [PATCH v2 0/4] KVM: x86: APICv cleanups Paolo Bonzini
2021-10-22 14:56 ` Maxim Levitsky
2021-10-22 16:43 ` Paolo Bonzini
2021-10-25 14:35 ` Sean Christopherson
2021-10-25 15:21 ` Paolo Bonzini
2021-10-25 15:59 ` Sean Christopherson [this message]
2021-10-25 16:05 ` Paolo Bonzini
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