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

Stefan Bader stefan.bader at
Tue Jan 8 13:43:34 UTC 2019

On 19.12.18 11:03, Juerg Haefliger wrote:
> git:// 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?

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>

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