[LAU] reducing xruns (System configuration)

Ralf Mardorf ralf.mardorf at alice-dsl.net
Fri Jul 20 11:56:51 CEST 2018


On Fri, 20 Jul 2018 11:24:57 +0200, David Kastrup wrote:
>So the idea to take this into low-latency realms with a view on
>realtime effects seems a bit optimistic indeed.

;)

On Thu, 19 Jul 2018 22:52:45 -1000, _another_ david wrote:
>I first tried it with 4.13.x and decided that items like random 
>kernel panios, system freezes and crashes weren't very good ways to 
>defend against Spectre/Meltdown/DOS. ;)

Actually freezes and crashes do defend against attacks :D. But you are
right, for Claws and Firefox I'm experiencing way to often serious
issues and for virtualbox at least way to often an annoyance for an
unexplained reason.

I at least should test using it with PTI disabled.

The current default on my machine is:

[rocketmouse at archlinux ~]$ ls -hAl /sys/devices/system/cpu/vulnerabilities/; cat /sys/devices/system/cpu/vulnerabilities/*
total 0
-r--r--r-- 1 root root 4.0K Jul 20 10:12 meltdown
-r--r--r-- 1 root root 4.0K Jul 20 10:12 spec_store_bypass
-r--r--r-- 1 root root 4.0K Jul 20 10:12 spectre_v1
-r--r--r-- 1 root root 4.0K Jul 20 10:12 spectre_v2
Mitigation: PTI
Vulnerable
Mitigation: __user pointer sanitization
Mitigation: Full generic retpoline, IBPB, IBRS_FW

'nopti' only would disable PTI, but keep the spectre mitigations. While
PTI is part of the kernel, the spectre mitigations are likely part
of the ┬Ácode. However, if I would run my CPU without the ┬Ácode, I
perhaps would get rid of the spectre mitigation, but IIRC I
unfortunately would get rid of TSC, too.


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