Messages in this thread | | | Date | Mon, 8 Jan 2018 13:47:07 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 4/8] x86/spec_ctrl: Add sysctl knobs to enable/disable SPEC_CTRL feature |
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On Fri, Jan 05, 2018 at 07:12:12PM -0800, Dave Hansen wrote: > On 01/05/2018 06:12 PM, Tim Chen wrote: > > .macro ENABLE_IBRS > > - ALTERNATIVE "jmp .Lskip_\@", "", X86_FEATURE_SPEC_CTRL > > + testl $1, dynamic_ibrs > > + jz .Lskip_\@ > > There was an earlier suggestion to use STATIC_JUMP_IF_... here. That's
Yes, and thanks for Cc'ing me... :/
> a good suggestion, but we encountered some issues with it either > crashing the kernel at boot or not properly turning on/off. > > We would love to do that minor really soon, but we figured everyone > would rather see this version than wait for us to debug such a minor tweak.
Its not minor, you need that LFENCE without it. Which makes the whole thing unconditionally expensive, which sucks.
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