Re: [PATCH 1/7] KVM: SVM: Initialize FRED VMCB fields

[Shivansh Dhiman]

Hi Christian,

On 14-03-2026 18:25, Christian Ludloff wrote:
>>> Is this architecturally correct?  I.e. are all the FRED MSRs zeroed on INIT?
>> Yes that's right, the FRED MSRs are zeroed on init.
> 
> Ahem... citation required, please.  :)
> 
> Because the FRED spec certainly claims otherwise:
> 
>   "The RESET state of each of the new MSRs is zero.
>   INIT does not change the value of the FRED MSRs."
> 
> See SDM vol3 #325384-090 @ end of section 8.2.3.
> 
> Getting initialized by INIT tends to be outlier behavior
> when it comes to MSRs – MPX, CET, EFER, FS/GS/
> kGS... but afaik the rest all remain unchanged.

Thanks for pointing this out. After consulting with the hardware folks, it
turns out the FRED MSRs are left unchanged on INIT. I had mistakenly mixed
up the INIT and RESET behavior. Apologies for the confusion.

I'll update the patch to only zero the FRED MSRs on RESET. Will address this
in v2.

Thanks,
Shivansh

> 
> And yes... this will need clarification from Intel... given
> that CET_PL0_SSP = FRED_SSP0_SL0... and it can
> not be both, unchanged and set-to-zero...  8-)
> 
> --
> C.