Messages in this thread | | | Date | Wed, 19 Oct 2022 11:01:41 -0700 | From | "H. Peter Anvin" <> | Subject | RE: [PATCH v4 5/5] x86/gsseg: use the LKGS instruction if available for load gs index() |
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On October 19, 2022 10:45:07 AM PDT, "Li, Xin3" <xin3.li@intel.com> wrote: >> > +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 >
Most things don't frob the paravirt list.
Maybe we should make the paravirt frobbing a separate patch, at it is separable.
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