Re: [PATCH] x86/bugs: Adjust SRSO mitigation to new features

[Borislav Petkov]

On Tue, Nov 05, 2024 at 10:10:20AM -0800, Sean Christopherson wrote:
> All of the actual maintainers.

Which maintainers do you mean? tip ones? If so, they're all shorted to
x86@xxxxxxxxxx.

> AFAIK, Paolo doesn't subscribe to kvm@.

Oh boy, srsly?! I thought I'd reach the proper crowd with
kvm@xxxxxxxxxxxxxxx...

> > Meh, I can split them if you really want me to.
> 
> I do.

Sure, next revision.

> What does the bit actually do?  I can't find any useful documentation, and the
> changelog is equally useless.


"Processors which set SRSO_MSR_FIX=1 support an MSR bit which mitigates SRSO
across guest/host boundaries. Software may enable this by setting bit
4 (BpSpecReduce) of MSR C001_102E. This bit can be set once during boot and
should be set identically across all processors in the system."

From: https://www.amd.com/content/dam/amd/en/documents/corporate/cr/speculative-return-stack-overflow-whitepaper.pdf

I think that's the only public info we have on that bit.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette