Re: [PATCH] x86/bhi: avoid hardware mitigation for 'spectre_bhi=vmexit'

[Pawan Gupta]

On Thu, Sep 12, 2024 at 03:44:38PM +0000, Jon Kohler wrote:
> > It is only worth implementing the long sequence in VMEXIT_ONLY mode if it is
> > significantly better than toggling the MSR.
> 
> Thanks for the pointer! I hadn’t seen that second sequence. I’ll do measurements on
> three cases and come back with data from an SPR system.
> 1. as-is (wrmsr on entry and exit)
> 2. Short sequence (as a baseline)
> 3. Long sequence

I wonder if virtual SPEC_CTRL feature introduced in below series can
provide speedup, as it can replace the MSR toggling with faster VMCS
operations:

  https://lore.kernel.org/kvm/20240410143446.797262-1-chao.gao@xxxxxxxxx/

Adding Chao for their opinion.