Re: [PATCH 0/7] KVM: SVM: Enable FRED support

[Shivansh Dhiman]

Hi Andrew,

On 11-02-2026 06:23, Andrew Cooper wrote:
>> Here is the newly published FRED virtualization spec by AMD for reference:
>>
>> 	https://docs.amd.com/v/u/en-US/69191-PUB
>>
>> Please feel free to share any feedback or questions.
> 
> 
> FYI, there is a fun behaviour captured in the sentence:
> 
> "If FRED virtualization is enabled, NMI virtualization must be enabled
> in order to properly handle guest NMIs"
> 
> i.e. hypervisors need to make sure not run the guest with FRED &&
> !vNMI.  AIUI, there's no ERETUx intercept similar to the IRET intercept
> with with to emulate NMI window tracking in !vNMI mode.

Thanks for letting me know about this. Seems like a legitimate consistency
check. I'll try to integrate it.

> 
> I requested that this become a VMRUN consistency check, but was
> declined.  I've asked that at least the wording change to "undefined
> behaviour" so something sane can be done for the nested case where L1
> tries to do something daft.
> 
> 
> There are two other issues which are going to be adjusted.  One is the
> consistency check concerning SS.DPL==3 && INTR_SHADOW==0 (not a valid
> restriction in later drafts of the spec), and one is "On an intercepted
> #DB, EXITINFO2 has DR6 register value."  Both do/will (not sure which)
> behave like Intel, rather than as currently documented.

Can you tell under which conditions does the #DB issue may arise?

> 
> ~Andrew

- Shivansh