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Subject: Re: [PATCH v2 1/3] KVM: x86: add support for user wait instructions
To:     Peter Zijlstra <peterz@infradead.org>, Tao Xu <tao3.xu@intel.com>
Cc:     rkrcmar@redhat.com, corbet@lwn.net, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
        sean.j.christopherson@intel.com, x86@kernel.org,
        kvm@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, jingqi.liu@intel.com
References: <20190524075637.29496-1-tao3.xu@intel.com>
 <20190524075637.29496-2-tao3.xu@intel.com>
 <20190527103003.GX2623@hirez.programming.kicks-ass.net>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <bcf669c8-81f4-0024-5f66-c40c6d519c62@redhat.com>
Date:   Wed, 29 May 2019 03:25:39 +0200
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On 27/05/19 12:30, Peter Zijlstra wrote:
>> This patch adds support for UMONITOR, UMWAIT and TPAUSE instructions
>> in kvm, and by default dont't expose it to kvm and provide a capability
>> to enable it.
>
> I'm thinking this should be conditional on the guest being a 1:1 guest,
> and I also seem to remember we have bits for that already -- they were
> used to disable paravirt spinlocks for example.

This should be userspace's choice.  It would indeed be silly to enable
this while overcommitted, but KVM doesn't really care.

Paolo