linux-kernel - Re: [PATCH v2 0/4] KVM: x86: APICv cleanups

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <674bc620-f013-d826-a4d4-00a142755a9e@redhat.com>
Date:   Mon, 25 Oct 2021 17:21:55 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Maxim Levitsky <mlevitsk@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/4] KVM: x86: APICv cleanups

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