[LAU] performance problems after kernel/microcode update ?

Ralf Mardorf ralf.mardorf at alice-dsl.net
Sat Sep 15 01:17:07 CEST 2018


On Fri, 14 Sep 2018 09:59:25 +0200, David Runge wrote:
>However, I would not advice you to disable mitigations such as page
>table isolation (PTI), unless you know about the implied risks!

Regarding Meltdown, loosely speaking, if the audio workstation is
connected to the Internet, we could boot without disabling PTI. If the
audio workstation is used for audio productions, we could boot with
disabling PTI and without connecting to the Internet. IIRC the
microcode for my CPU not only is required for Spectre mitigation, but
also to make TSC available and perhaps to fix other CPU issues, too, so
there might be no option to boot without the microcode at all.

The '/sys/devices/system/cpu/vulnerabilities/*' "list" is increasing ;).

[rocketmouse at archlinux ~]$ uname -a
Linux archlinux 4.18.7-rt5-1-rt-securityink #1 SMP PREEMPT RT Thu Sep 13 08:01:15 CEST 2018 x86_64 GNU/Linux
[rocketmouse at archlinux ~]$ dmesg | grep micro
[    0.000000] microcode: microcode updated early to revision 0x25, date = 2018-04-02
[    0.457030] microcode: sig=0x306c3, pf=0x2, revision=0x25
[    0.457083] microcode: Microcode Update Driver: v2.2.
[rocketmouse at archlinux ~]$ ls -l /sys/devices/system/cpu/vulnerabilities/*
-r--r--r-- 1 root root 4096 Sep 15 01:12 /sys/devices/system/cpu/vulnerabilities/l1tf
-r--r--r-- 1 root root 4096 Sep 15 01:12 /sys/devices/system/cpu/vulnerabilities/meltdown
-r--r--r-- 1 root root 4096 Sep 15 01:12 /sys/devices/system/cpu/vulnerabilities/spec_store_bypass
-r--r--r-- 1 root root 4096 Sep 15 01:12 /sys/devices/system/cpu/vulnerabilities/spectre_v1
-r--r--r-- 1 root root 4096 Sep 15 01:12 /sys/devices/system/cpu/vulnerabilities/spectre_v2
[rocketmouse at archlinux ~]$ cat  /sys/devices/system/cpu/vulnerabilities/*
Mitigation: PTE Inversion; VMX: conditional cache flushes, SMT disabled
Mitigation: PTI
Mitigation: Speculative Store Bypass disabled via prctl and seccomp
Mitigation: __user pointer sanitization
Mitigation: Full generic retpoline, IBPB, IBRS_FW


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