Messages in this thread | | | From | "Li, Xin3" <> | Subject | RE: [PATCH v4 5/5] x86/gsseg: use the LKGS instruction if available for load_gs_index() | Date | Wed, 19 Oct 2022 17:45:07 +0000 |
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> > +static inline void __init lkgs_init(void) { #ifdef > > +CONFIG_PARAVIRT_XXL #ifdef CONFIG_X86_64 > > + if (cpu_feature_enabled(X86_FEATURE_LKGS)) > > + pv_ops.cpu.load_gs_index = native_lkgs; > > For this to work correctly when running as a Xen PV guest, you need to add > > setup_clear_cpu_cap(X86_FEATURE_LKGS); > > to xen_init_capabilities() in arch/x86/xen/enlighten_pv.c, as otherwise the Xen > specific .load_gs_index vector will be overwritten.
Yeah, we definitely should add it to disable LKGS in a Xen PV guest.
So does it mean that the Xen PV uses a black list during feature detection? If yes then new features are often required to be masked with an explicit call to setup_clear_cpu_cap.
Wouldn't a white list be better? Then the job is more just on the Xen PV side, and it can selectively enable a new feature, sometimes with Xen PV specific handling code added.
Xin
> > > Juergen
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