Re: [Xen-devel] [PATCH 06/10] x86/spec_ctrl: Split X86_FEATURE_SC_MSR into PV and HVM variants

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.05.18 at 12:38, <andrew.cooper3@xxxxxxxxxx> wrote:
> --- a/xen/arch/x86/spec_ctrl.c
> +++ b/xen/arch/x86/spec_ctrl.c
> @@ -128,7 +128,8 @@ static void __init print_details(enum ind_thunk thunk, 
> uint64_t caps)
>             thunk == THUNK_RETPOLINE ? "RETPOLINE" :
>             thunk == THUNK_LFENCE    ? "LFENCE" :
>             thunk == THUNK_JMP       ? "JMP" : "?",
> -           boot_cpu_has(X86_FEATURE_SC_MSR) ?
> +           (boot_cpu_has(X86_FEATURE_SC_MSR_PV) ||
> +            boot_cpu_has(X86_FEATURE_SC_MSR_HVM)) ?
>             default_xen_spec_ctrl & SPEC_CTRL_IBRS    ? " IBRS+" :
>                                                         " IBRS-"      : "",
>             opt_ibpb                                  ? " IBPB"       : "",
> @@ -367,7 +368,8 @@ void __init init_speculation_mitigations(void)
>           * need the IBRS entry/exit logic to virtualise IBRS support for
>           * guests.
>           */
> -        setup_force_cpu_cap(X86_FEATURE_SC_MSR);
> +        setup_force_cpu_cap(X86_FEATURE_SC_MSR_PV);
> +        setup_force_cpu_cap(X86_FEATURE_SC_MSR_HVM);

Besides these sort of open coding alternative_io_2() (you'd really want an
output-less variant here, I agree) these are slightly bending the rules of
when/how to use multiple alternatives: The above ends up correct only
because of both replacements being identical.

Jan



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