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From: Paolo Bonzini <pbonzini@redhat.com>
To: Xiaoyao Li <xiaoyao.li@intel.com>,
	Wanpeng Li <kernellwp@gmail.com>,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: Sean Christopherson <sean.j.christopherson@intel.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>
Subject: Re: [PATCH] KVM: X86: Expose KVM_HINTS_REALTIME in KVM_GET_SUPPORTED_CPUID
Date: Thu, 22 Oct 2020 16:44:52 +0200	[thread overview]
Message-ID: <4a5d0ccd-f6a7-2afe-2480-991ff7e079b4@redhat.com> (raw)
In-Reply-To: <18e7a0c6-faff-8c4c-0830-a0bc02627a36@intel.com>

On 22/10/20 16:28, Xiaoyao Li wrote:
> On 10/22/2020 10:06 PM, Paolo Bonzini wrote:
>> On 22/10/20 15:31, Xiaoyao Li wrote:
>>>>
>>>> It's common for userspace to copy all supported CPUID bits to
>>>> KVM_SET_CPUID2, I don't think this is the right behavior for
>>>> KVM_HINTS_REALTIME.
>>>
>>> It reminds of X86_FEATURE_WAITPKG, which is added to supported CPUID
>>> recently as a fix but QEMU exposes it to guest only when "-overcommit
>>> cpu-pm"
>>
>> WAITPKG is not included in KVM_GET_SUPPORTED_CPUID either.  QEMU detects
>> it through the MSR_IA32_UMWAIT register.
> 
> Doesn't 0abcc8f65cc2 ("KVM: VMX: enable X86_FEATURE_WAITPKG in KVM
> capabilities") add WAITPKG to KVM_GET_SUPPORTED_CPUID?

You're right, I shouldn't have checked only cpuid.c. :)

Still I think WAITPKG is different, because it's only for userspace and
it's always possible for userspace to do "for(;;)" and burn CPU.
KVM_HINTS_REALTIME is more similar to MONITOR, which is not set.

Paolo


  reply	other threads:[~2020-10-22 14:45 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-22  1:34 [PATCH] KVM: X86: Expose KVM_HINTS_REALTIME in KVM_GET_SUPPORTED_CPUID Wanpeng Li
2020-10-22 13:02 ` Paolo Bonzini
2020-10-22 13:25   ` Vitaly Kuznetsov
2020-10-22 13:31   ` Xiaoyao Li
2020-10-22 14:06     ` Paolo Bonzini
2020-10-22 14:28       ` Xiaoyao Li
2020-10-22 14:44         ` Paolo Bonzini [this message]
2020-10-22 16:35   ` Jim Mattson
2020-10-22 16:37     ` Paolo Bonzini
2020-10-22 17:13       ` Jim Mattson
2020-10-23  9:07         ` Paolo Bonzini
2020-10-23 17:03           ` Jim Mattson
2020-10-23  0:27   ` Wanpeng Li

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