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

[Juerg Haefliger]

On Tue, 8 Jan 2019 14:43:34 +0100
Stefan Bader <stefan.bader at canonical.com> 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

spec_ctrl_mutex is already defined (introduced by the original IBRS/IBPB
patches).


> but only
> "UBUNTU: SAUCE: x86/speculation: Cleanup IBRS runtime control handling" which
> follows next actually seems to declare it.

That patch just moves the definition from kernel/smp.c to kernel/sysctl.c.


> In the end that does not matter only
> could make bisection a pain.


IIRC, I've compile-tested every single patch.

 
> Minor pedantic nitbit: is not "UBUNTU: SAUCE: x86/speculation: Move RSB_CTXSW
> hunk" moving the hunk further down?

Nope. The diff shows a different hunk being moved down as a result of moving
RSB_CTXSW up. So the title is misleading and should probably read 'Move
X86_FEATURE_IBPB hunk'.

...Juerg


> Apart from that the other changes roughly seemed to make sense but I have to
> admit that I went rather quickly over the non-SAUCE ones. The delta is just too
> big and I rely a bit on the successful testing.
> 
> So if fixing up the first 2 patches (which should be doable when applying)
> 
> Acked-by: Stefan Bader <stefan.bader at canonical.com>
> 

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