linux-kernel - Re: [PATCH] KVM: X86: Expose KVM_HINTS_REALTIME in KVM_GET_SUPPORTED

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Message-ID: <6ad94df6-9ecd-e364-296a-34ba41e938b1@intel.com>
Date:   Thu, 22 Oct 2020 21:31:23 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH] KVM: X86: Expose KVM_HINTS_REALTIME in
 KVM_GET_SUPPORTED_CPUID

On 10/22/2020 9:02 PM, Paolo Bonzini wrote:
> On 22/10/20 03:34, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpengli@...cent.com>
>>
>> Per KVM_GET_SUPPORTED_CPUID ioctl documentation:
>>
>> This ioctl returns x86 cpuid features which are supported by both the
>> hardware and kvm in its default configuration.
>>
>> A well-behaved userspace should not set the bit if it is not supported.
>>
>> Suggested-by: Jim Mattson <jmattson@...gle.com>
>> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> 
> 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"

> (But maybe this was discussed already; if so, please point me to the
> previous discussion).
> 
> Paolo
>