linux-kernel - Re: [PATCH resend] x86,kvm: Add a kernel parameter to disable PV spinlock

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Message-ID: <e0217f29-7807-fbdb-a2f6-fb8705aa4f73@redhat.com>
Date:   Mon, 4 Sep 2017 15:32:39 -0400
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Oscar Salvador <osalvador@...e.de>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH resend] x86,kvm: Add a kernel parameter to disable PV
 spinlock

On 09/04/2017 10:40 AM, Peter Zijlstra wrote:
> On Mon, Sep 04, 2017 at 04:28:36PM +0200, Oscar Salvador wrote:
>> This is just a resend of Waiman Long's patch.
>> I could not find why it was not merged to upstream, so I thought
>> to give it another chance.
>> What follows is what Waiman Long wrote.
>>
>> Xen has an kernel command line argument "xen_nopvspin" to disable
>> paravirtual spinlocks. This patch adds a similar "kvm_nopvspin"
>> argument to disable paravirtual spinlocks for KVM. This can be useful
>> for testing as well as allowing administrators to choose unfair lock
>> for their KVM guests if they want to.
> For testing its trivial to hack your kernel and I don't feel this is
> something an Admin can make reasonable decisions about.

I almost forgot about this patch that I sent quite a while ago. I was
sending this patch out mainly to maintain consistency between KVM and
Xen. This patch is not that important to me, and that is why I didn't
push it further.

Cheers,
Longman