linux-kernel - Re: [patch 0/3] KVM CPU frequency change hypercalls

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: <5db0e1a1-2eaf-fe77-3e15-7b2ef842d255@redhat.com>
Date:   Thu, 23 Feb 2017 18:35:24 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Radim Krcmar <rkrcmar@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [patch 0/3] KVM CPU frequency change hypercalls



On 03/02/2017 20:09, Radim Krcmar wrote:
> One reason why we have a kernel/userspace split is to allow sharing of
> CPU time.  Each application then its state that the kernel keeps track
> of and saves/restores while time-multiplexing.
> 
> Our frequency scaling interface goes against the idea -- guest kernel
> cannot schedule multiple userspaces on the same vCPU, because they could
> conflict by overriding frequency.
> 
> i.e. our feature implies userspace tasks pinned to isolated vCPUs.

That's bad.  This feature is broken by design unless it does proper
save/restore across preemption.

You don't need a hypercall.  Add a cpufreq driver in DPDK that doesn't
use sysfs, and connect it to a daemon in the host through virtio-serial
or vsock.

Paolo