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

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Message-ID: <aW83vbC2KB6CZDvl@intel.com>
Date: Tue, 20 Jan 2026 16:07:25 +0800
From: Chao Gao <chao.gao@...el.com>
To: Xin Li <xin@...or.com>
CC: <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

On Mon, Jan 19, 2026 at 10:56:29PM -0800, Xin Li wrote:
>
>
>> On Nov 11, 2025, at 11:30 PM, Chao Gao <chao.gao@...el.com> wrote:
>> 
>> I'm not sure if AMD CPUs support FRED, but just in case, we can clear FRED
>> i.e., kvm_cpu_cap_clear(X86_FEATURE_FRED) in svm_set_cpu_caps().
>
>AMD will support FRED, with ISA level compatibility:
>
>https://www.amd.com/en/blogs/2025/amd-and-intel-celebrate-first-anniversary-of-x86-ecosys.html
>
>Thus we don’t need to clear the bit.

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.