linux-kernel - Re: [PATCH v3 2/8] KVM: Register cpuhp and syscore callbacks when enabling hardware

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: <Zr0ZwZsSEqSH5mQN@google.com>
Date: Wed, 14 Aug 2024 13:55:29 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Chao Gao <chao.gao@...el.com>, Kai Huang <kai.huang@...el.com>
Subject: Re: [PATCH v3 2/8] KVM: Register cpuhp and syscore callbacks when
 enabling hardware

On Wed, Aug 14, 2024, Paolo Bonzini wrote:
> On 6/8/24 02:06, Sean Christopherson wrote:
> > Register KVM's cpuhp and syscore callback when enabling virtualization
> > in hardware instead of registering the callbacks during initialization,
> > and let the CPU up/down framework invoke the inner enable/disable
> > functions.  Registering the callbacks during initialization makes things
> > more complex than they need to be, as KVM needs to be very careful about
> > handling races between enabling CPUs being onlined/offlined and hardware
> > being enabled/disabled.
> > 
> > Intel TDX support will require KVM to enable virtualization during KVM
> > initialization, i.e. will add another wrinkle to things, at which point
> > sorting out the potential races with kvm_usage_count would become even
> > more complex.
> > 
> > Note, using the cpuhp framework has a subtle behavioral change: enabling
> > will be done serially across all CPUs, whereas KVM currently sends an IPI
> > to all CPUs in parallel.  While serializing virtualization enabling could
> > create undesirable latency, the issue is limited to creation of KVM's
> > first VM,
> 
> Isn't that "limited to when kvm_usage_count goes from 0 to 1", so every time
> a VM is started if you never run two?

Yes, "first" isn't the correct word/phrase.