Re: [PATCH 4.19 041/361] x86/speculation: Enable cross-hyperthread spectre v2 STIBP mitigation

Tim Chen
2018-11-21T17:47:50Z

On 11/21/2018 05:56 AM, Greg Kroah-Hartman wrote:
> On Wed, Nov 21, 2018 at 02:21:15PM +0100, Jiri Kosina wrote:
>> On Sun, 11 Nov 2018, Greg Kroah-Hartman wrote:
>>
>>> 4.19-stable review patch. If anyone has any objections, please let me know.
>>
>> Greg, please drop this patch from all -stable for now. Version that
>> wouldn't have such performance impact is being worked on.
>
> Is it reverted in Linus's tree? If not, then anything that comes "later
> on" will not apply here, right?
>
> I see the thread asking about this, but I got really conflicting
> messages here, and now it's in all of the latest releases, and no
> testing seems to have uncovered issues. Is it just a "slow down"
> problem?

Greg,

It could be a big slow down in excess of 20% for some applications.
And cross sibling Spectre v2 attack is quite hard to pull off.

So till we have the accompanying patchset that only apply STIBP on processes
that really need it instead of universally, it should be withheld from
stable.

Tim