From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <seanjc@google.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 17:21:55 +0200 [thread overview]
Message-ID: <674bc620-f013-d826-a4d4-00a142755a9e@redhat.com> (raw)
In-Reply-To: <YXbAxkf1W37m9eZp@google.com>
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.
Therefore it makes sense for the page fault path to synchronize with
whoever updates the flag and zaps the page, and not with the KVM_REQ_*
handler of the same vCPU.
(Here goes the usual shameless plug of my lockless programming articles
on LWN---I think you're old enough to vaguely remember Jerry
Pournelle---and in particular the first one at
https://lwn.net/Articles/844224/).
> Want me to type up a v3 comment?
Yes, please do.
Paolo
next prev parent reply other threads:[~2021-10-25 15:22 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-22 0:49 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 [this message]
2021-10-25 15:59 ` Sean Christopherson
2021-10-25 16:05 ` Paolo Bonzini
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