ACK/Cmnt: [SRU][Xenial][PULL] Guests using IBRS incur a large performance penalty (LP: #1764956)

[Stefan Bader]

On 09.01.19 10:56, Juerg Haefliger wrote:
> On Tue, 8 Jan 2019 18:34:35 +0100
> Kleber Souza <kleber.souza at canonical.com> wrote:
> 
>> On 1/8/19 2:43 PM, Stefan Bader wrote:
>>> On 19.12.18 11:03, Juerg Haefliger wrote:  
>>>> git://git.launchpad.net/~juergh/+git/xenial-linux lp1764956-v2  
>>>
>>> Glancing over the changes I noticed that "UBUNTU: SAUCE: x86/speculation:
>>> Cleanup IBPB runtime control handling" adds use of spec_ctrl_mutex but only
>>> "UBUNTU: SAUCE: x86/speculation: Cleanup IBRS runtime control handling" which
>>> follows next actually seems to declare it. In the end that does not matter only
>>> could make bisection a pain.
>>>
>>> Minor pedantic nitbit: is not "UBUNTU: SAUCE: x86/speculation: Move RSB_CTXSW
>>> hunk" moving the hunk further down?  
>>
>> The mentioned commits, although they are on that branch, are not part of
>> this PR (which is only
>> d0b9a387cf1d68745c558d04fd3aa980497d1529..7ad0e9a99c1466f8fee92cba5ffeaa0af83f6622).
>> They seem to have been sent as part of an earlier thread titled
>> "[SRU][Xenial][PATCH v2 0/4] Cleanups for CVE-2017-5715 (Spectre v2)".
> 
> Ah yes. That's a different patchset unrelated to the issue that the PR fixes.
> They just happen to be both IBRS/IBPB code changes.
> 
>  
>> Should we treat these patches as separated requests or as a single PR?
> 
> Separately please. And somebody please review the assembly code changes
> (patch 3/4)... There are probably better ways to do this but my assembly foo
> isn't that stellar  :-)

I did (but should respond about that to the other thread, I did not notice I
went out of bounds yesterday). I think after a long time of head scratching
those seemed to make sense. The whole r?x vs. e?x business is just
architecturally ugly.

> 
> ...Juerg
> 
> 
> 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 833 bytes
Desc: OpenPGP digital signature
URL: <https://lists.ubuntu.com/archives/kernel-team/attachments/20190109/220629d2/attachment.sig>