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

[Juerg Haefliger]

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  :-)

...Juerg



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