Bug 904035

Summary:	[EXPERIMENTAL] sys-kernel/gentoo-sources & sys-kernel/vanilla-sources => Patchset for automatic IBRS backported from Linux 6.3 to Linux 6.2(.10)
Product:	Gentoo Linux	Reporter:	Adrien Dessemond <admnd>
Component:	Current packages	Assignee:	Gentoo Kernel Bug Wranglers and Kernel Maintainers <kernel>
Status:	RESOLVED FIXED
Severity:	enhancement
Priority:	Normal
Version:	unspecified
Hardware:	AMD64
OS:	Linux
Whiteboard:
Package list:		Runtime testing required:	---
Attachments:	Patchset for automatic IBRS retrofitted for Linux 6.2.10

Description Adrien Dessemond 2023-04-08 14:50:44 UTC

Kernel 6.3 brings the support of auto-IBRS (AMD Zen 4 processors). However I am stuck with kernel 6.2 series due to a WIP in OpenZFS 2.1.x to support the 6.3 kernel series which, I guess, will take awhile as internal kernel's API has changed in-between.

In the meantime, I managed to retrofit this => https://lore.kernel.org/lkml/20230124163319.2277355-1-kim.phillips@amd.com for sys-kernel/gentoo-sources:6.2.10 (AFAK their v9 is the more recent work in the subject at time of writing).

Various pieces are spread amongst the discussion nevertheless I am confident that all pieces have been put together.

So far the 6.2(.10) kernel can be built and boots normally without any issues :)

And... 


# dmesg  | grep Spectre
[    0.228161] Spectre V1 : Mitigation: usercopy/swapgs barriers and __user pointer sanitization
[    0.228163] Spectre V2 : Mitigation: Enhanced / Automatic IBRS
[    0.228164] Spectre V2 : Spectre v2 / SpectreRSB mitigation: Filling RSB on context switch
[    0.228166] Spectre V2 : mitigation: Enabling conditional Indirect Branch Prediction Barrier

Not tested stability with KVM virtual machines so far but feel free to experiment ;)

Comment 1 Adrien Dessemond 2023-04-08 14:54:57 UTC

Created attachment 859690 [details, diff]
Patchset for automatic IBRS retrofitted for Linux 6.2.10

See bug description. The work is based on a Linux 6.2.10 kernel, not sure it will be applicable as-is for future Linux 6.2.x releases.

Comment 2 Adrien Dessemond 2023-04-09 13:34:49 UTC

Can also be applied over a 6.2.6 to 6.2.9 kernel as well according to my tests and probably all earlier 6.2 series kernels (untested).

Does not work with 6.1 and earlier kernel series.

Comment 3 Mike Pagano gentoo-dev

2023-04-11 15:25:48 UTC

(In reply to Adrien Dessemond from comment #2)
> Can also be applied over a 6.2.6 to 6.2.9 kernel as well according to my
> tests and probably all earlier 6.2 series kernels (untested).
> 
> Does not work with 6.1 and earlier kernel series.

Thank-you for your contribution.  There's still a lot of conversation on this with debate on how to do things.

I'd like to wait a bit before we carry this one.

Comment 4 Mike Pagano gentoo-dev

2023-07-02 17:26:45 UTC

IBRS came with 6.3 and 6.2 is EOL.  Closing this one.