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

[Xin Li]

> On Jan 20, 2026, at 7:25 AM, Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
> 
>>> 
>>> What I have missed?
> 
> The userspace VMM, e.g. QEMU, is completely irrelevant.  KVM must not advertise
> support for features it doesn't actually implement, and more importantly must not
> internally treat such features as supported.

Right, FRED virtualization is not supported on AMD and obviously SVM will
need to add FRED virtualization in their own fashion later.

> 
>> 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.
> 
> Yep.
> 
>> I guess it's no safety issue for host though,
> 
> Maybe.  Without fully analyzing the SVM implementation for FRED and its interaction
> with KVM, I don't think we can confidently say that incorrectly treating FRED as
> supported is benign for the host.  It's a moot point, I just want to emphasize
> how it important it is that KVM doesn't over-report features.

I will remove it on AMD.