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Subject: Re: [PATCH v2 1/3] KVM: x86: add support for user wait instructions
To:     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>
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 <419f62f3-69a8-7ec0-5eeb-20bed69925f2@redhat.com>
 <c1b27714-2eb8-055e-f26c-e17787d83bb6@intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <b5daf72d-d764-baa4-8e7f-b09dff417786@redhat.com>
Date:   Wed, 29 May 2019 04:38:53 +0200
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On 29/05/19 04:05, Tao Xu wrote:
>>
> 
> Thank you Paolo, but I have another question. I was wondering if it is
> appropriate to enable X86_FEATURE_WAITPKG when QEMU uses "-overcommit
> cpu-pm=on"?

"-overcommit" only establishes the behavior of KVM, it doesn't change
the cpuid bits.  So you'd need "-cpu" as well.

Paolo

> Or just enable X86_FEATURE_WAITPKG when QEMU add the feature
> "-cpu host,+waitpkg"? User wait instructions is the wait or pause
> instructions may be executed at any privilege level, but can use
> IA32_UMWAIT_CONTROL to set the maximum time.