linux-kernel - Re: [PATCH v9 17/22] KVM: x86: Advertise support for FRED

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Message-Id: <C6C0D514-BCE0-4ADD-9110-3FC7A2E813F8@zytor.com>
Date: Tue, 20 Jan 2026 09:58:40 -0800
From: Xin Li <xin@...or.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
Cc: Chao Gao <chao.gao@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org, pbonzini@...hat.com,
        seanjc@...gle.com, corbet@....net, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, luto@...nel.org, peterz@...radead.org,
        andrew.cooper3@...rix.com, hch@...radead.org, sohil.mehta@...el.com
Subject: Re: [PATCH v9 17/22] KVM: x86: Advertise support for FRED

>>> 
>>> In this case, we need to clear FRED for AMD.
>>> 
>>> The concern is that before AMD's FRED KVM support is implemented, FRED will be
>>> exposed to userspace on AMD FRED-capable hardware. This may cause issues.
>> 
>> Hmm, I think it’s Qemu does that.
>> 
>> We have 2 filters, one in Qemu and one in KVM, only both are set a feature is enabled.
>> 
>> What I have missed?
> 
> If a newer QEMU (with AMD's FRED support patch) + an older KVM (without AMD's
> FRED support, but KVM advertises it), it may cause issues.
> 
> I guess it's no safety issue for host though, AMD should also require some
> control bit(s) to be set to allow guests to use the feature.
> 
> I agree with Chao that it should be cleared for AMD before AMD's FRED KVM
> support is implemented.


Damn, I somehow thought the host won’t report FRED on AMD...