Re: Linux 4.14: Reported regressions as of Sunday, 2017-10-08

[Adam Borowski]

On Sun, Oct 08, 2017 at 02:37:41PM +0200, Thorsten Leemhuis wrote:
> Hi! Find below my second regression report for Linux 4.14. It lists 8
> regressions I'm currently aware of. One regression was fixed since last
> weeks report. One was in there that shouldn't have been there.
> 
> == Current regressions ==
> 
> "hangs when building e.g. perf" & "Random insta-reboots on AMD Phenom II"
> Status: "Mr. Luto better revert the new lazy TLB flushing fun'n'games"
> -> "Yeah, working on it.  It's not a straightforward revert."
> Note: TWIMC: Workaround: wrmsr -a 0xc0010015 0x1000018
> Reported: 2017-09-05
> https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg1484723.html
> https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg1501379.html
> https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg1501570.html
> Cause: 94b1b03b519b81c494900cb112aa00ed205cc2d9

Uhm, that particular register value in the workaround applies only to a
particular CPU, and it sounds dangerous to use it as-is otherwise.

On affected families (apparently 15h as well) it's bit 0x00000008 in
register 0xc0010015, you need to rdmsr that register then or that bit with
whatever value you had before.

(And I have no clue about how it works -- merely repeating what the guys say.
You'd want to not do so blindly.)


Meow!
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