> The feature strings are automatically generated from the define. The comment > can be used to supress them by an empty "" string or to modify them by a > "override" string at the beginning of the comment.
I overlooked "override" part. Sorry! about that. It's clear now. Thanks for the explanation. > > > > > > + WARN_ON_ONCE(x86_spec_ctrl_base & SPEC_CTRL_IBRS); > > Please remove the warnon as well. > Sure! I removed it but forgot to mention it. > > > > + /* Ensure SPEC_CTRL_IBRS is set after VMEXIT from a guest */ > > > > + x86_spec_ctrl_base |= SPEC_CTRL_IBRS; > > > > > > And what exactly writes the MSR? > > > > > > > While booting, x86_spec_ctrl_setup_ap() does that and after VMEXIT > > x86_spec_ctrl_restore_host(). > > > > As x86_spec_ctrl_setup_ap() does wrmsrl(MSR_IA32_SPEC_CTRL, > > x86_spec_ctrl_base), I thought writing here would be redundant. > > x86_spec_ctrl_setup_ap() is only called on the AP but not on the BP. So the > boot > processor will not have it set, unless something else writes the MSR. So you > really want to have an explicit write there. Yes, that makes sense. But on the machine, I see IBRS bit set on all cores. As you said, someone else might be writing the MSR. I will try to find that out and will update the patch accordingly. I initially suspected it to be __ssb_select_mitigation() as I have "spec_store_bypass_disable=on" in the kernel command line, but turns out it's not so. I will update you more on this. Regards, Sai
