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SubjectRe: [PATCH] x86/speculation: Revert turning on STIBP all the time
On Wed, 21 Nov 2018, Tim Chen wrote:

> Commit 53c613fe "x86/speculation: Enable cross-hyperthread spectre v2 STIBP mitigation"
> turns on STIBP all the time.
>
> This causes large performance regression in many workloads.
>
> One case is perlbench in the SpecInt Rate 2006 test suite which shows a
> 21% reduction in throughput.
> There're also other reports of drop in performance on Python and PHP benchmarks:
> https://www.phoronix.com/scan.php?page=article&item=linux-420-bisect&num=2
>
> STIBP on all the time should not be the default option.
>
> Turn off STIBP all the time for now till STIBP can be applied on
> a per task basis.
>
> Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
> ---
> arch/x86/kernel/cpu/bugs.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index c37e66e..21a8f39 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -332,7 +332,7 @@ static bool stibp_needed(void)
> if (!boot_cpu_has(X86_FEATURE_STIBP))
> return false;
>
> - return true;
> + return false;
> }

For -stable, which actually makes it to production, I already asked Greg
to drop it.

For -rc, I don't think we need to do this at this moment, given the
prctl+seccomp fixup is basically ready, do we?

Thanks,

--
Jiri Kosina
SUSE Labs

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