News: 0001541964

  ARM Give a man a fire and he's warm for a day, but set fire to him and he's warm for the rest of his life (Terry Pratchett, Jingo)

Linux Being Patched For Buggy MWAIT Behavior On Intel Ice Lake Servers

([Intel] 5 Hours Ago Buggy MWAIT)


The Linux kernel has seen safeguards for select prior Intel CPU cores due to bugs around the MONITOR/MWAIT implementation with the processors. MWAIT/MONITOR bugs was found to be the cause of [1]annoying issues at boot for Lunar Lake laptops and also previously plagued Goldmont Atom cores. It also turns out that Ice Lake servers can be subject to similar MWAIT/MONITOR behavior.

Surprisingly it's taken until now for this issue to creep up and be fixed soon in the mainline Linux kernel. After all, 3rd Gen Xeon Scalable "Ice Lake" [2]launched back in 2021 .

Intel via a specification document update sent out a notice in 2022 that their 3rd Gen Xeon Scalable "Ice Lake" server processors indeed had a known issue where MONITOR may not be triggered that was armed via the MWAIT instruction. In turn this can lead to a processor hang as noted in the ICX143 spec update.

Finally in 2025 this is being patched by the Linux kernel in the same manner as the Lunar Lake and Goldmont to avoid the MWAIT issue. This CPU bug has been hitting server folks now at least under some Xen virtualization usage. [3][PATCH] Handle Ice Lake MONITOR erratum was posted yesterday and explained:

"Andrew Cooper reported some boot issues on Ice Lake servers when running Xen that he tracked down to MWAIT not waking up. Do the safe thing and consider them buggy since there's a published erratum. Note: I've seen no reports of this occurring on Linux.

Add Ice Lake servers to the list of shaky MONITOR implementations with no workaround available."

Hopefully the future Intel CPU cores will have less worries around their MONITOR/MWAIT handling but at least for this Xeon Ice Lake issue doesn't seem to be too common unlike the Lunar Lake issues that came up shortly after launch.

This Ice Lake patch is currently for review on the Linux kernel mailing list but will likely be submitted in the coming days or so as part of fixes to Linux 6.15 and then back-ported.



[1] https://www.phoronix.com/news/Intel-Lunar-Lake-Monitor-Bug

[2] https://www.phoronix.com/review/intel-xeon-8380-linux

[3] https://lore.kernel.org/lkml/20250421192205.7CC1A7D9@davehans-spike.ostc.intel.com/


reba

Michael

ultimA

The Poet Whose Badness Saved His Life
The most important poet in the seventeenth century was George
Wither. Alexander Pope called him "wretched Wither" and Dryden said of his
verse that "if they rhymed and rattled all was well".
In our own time, "The Dictionary of National Biography" notes that his
work "is mainly remarkable for its mass, fluidity and flatness. It usually
lacks any genuine literary quality and often sinks into imbecile doggerel".
High praise, indeed, and it may tempt you to savour a typically
rewarding stanza: It is taken from "I loved a lass" and is concerned with
the higher emotions.
She would me "Honey" call,
She'd -- O she'd kiss me too.
But now alas! She's left me
Falero, lero, loo.
Among other details of his mistress which he chose to immortalize
was her prudent choice of footwear.
The fives did fit her shoe.
In 1639 the great poet's life was endangered after his capture by
the Royalists during the English Civil War. When Sir John Denham, the
Royalist poet, heard of Wither's imminent execution, he went to the King and
begged that his life be spared. When asked his reason, Sir John replied,
"Because that so long as Wither lived, Denham would not be accounted the
worst poet in England."
-- Stephen Pile, "The Book of Heroic Failures"