Re: [Qemu-devel] cpu.fail / MDS fixes

[Stefan Priebe - Profihost AG]

Am 15.05.19 um 19:54 schrieb Daniel P. Berrangé:
> On Wed, May 15, 2019 at 07:13:56PM +0200, Stefan Priebe - Profihost AG wrote:
>> Hello list,
>>
>> i've updated my host to kernel 4.19.43 and applied the following patch
>> to my qemu 2.12.1:
>> https://bugzilla.suse.com/attachment.cgi?id=798722
>>
>> But my guest running 4.19.43 still says:
>> Vulnerable: Clear CPU buffers attempted, no microcode; SMT Host state
>> unknown
>>
>> while the host says:
>> Vulnerable: Clear CPU buffers attempted, SMT Host state unknown
> 
> That suggests your host OS hasn't got the new microcode installed
> or has not loaded it.

No it does not. A not loaded Microcode looks like this:
Vulnerable: Clear CPU buffers attempted, no microcode; SMT vulnerable

but in my case it is:
Mitigation: Clear CPU buffers; SMT vulnerable

on the host as hyper threading is still enabled.

> You want the host to report that it is Mitigated, and for the
> host's /proc/cpuinfo to report "md-clear" exists.
> 
>> I expected the guest can use the new microcode.
> 
> You've not said what CPU model you've given to the guest.
> 
> You need either "-cpu host", or if using a named CPU model
> you need to explicitly turn on the "md-clear" feature
> (and all previous fixes)
> 
>    eg  "-cpu Haswell,+spec-ctrl,+ssbd,+md-clear"
hah yes you're true i need to specifiy +md-clean

Thanks!

> Regards,
> Daniel
>