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SubjectRe: [tip:x86/pti] Revert "x86/speculation: Simplify indirect_branch_prediction_barrier()"

* Peter Zijlstra <peterz@infradead.org> wrote:

>
> On Tue, Feb 13, 2018 at 12:58:21AM -0800, tip-bot for David Woodhouse wrote:
>
> > --- a/arch/x86/include/asm/nospec-branch.h
> > +++ b/arch/x86/include/asm/nospec-branch.h
> > @@ -164,10 +164,15 @@ static inline void vmexit_fill_RSB(void)
> >
> > static inline void indirect_branch_prediction_barrier(void)
> > {
> > + asm volatile(ALTERNATIVE("",
> > + "movl %[msr], %%ecx\n\t"
> > + "movl %[val], %%eax\n\t"
> > + "movl $0, %%edx\n\t"
> > + "wrmsr",
> > + X86_FEATURE_USE_IBPB)
> > + : : [msr] "i" (MSR_IA32_PRED_CMD),
> > + [val] "i" (PRED_CMD_IBPB)
> > + : "eax", "ecx", "edx", "memory");
> > }
>
> Joe Konno pointed out that we now need the below line too, because we're
> using MSR_IA32_PRED_CMD in this header.
>
> With the existing code that's not a problem per-se, but my objtool
> retpoline annotation things did do stumble over this.
>
> Do we want to fold it into the objtool annotation patch or have it
> separate?

Separate would be better, it makes sense and is one problem less to worry about?

Thanks,

Ingo

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