linux-kernel - Re: [regression/bisected] Add IBPB decreases performance in two times

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Message-ID: <20230813082413.GAZNiTLaOxUNUHPvlf@fat_crate.local>
Date:   Sun, 13 Aug 2023 10:24:13 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
Cc:     Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        x86@...nel.org
Subject: Re: [regression/bisected] Add IBPB decreases performance in two times

On Sun, Aug 13, 2023 at 03:55:11AM +0500, Mikhail Gavrilov wrote:
> Hi,
> I use Fedora Rawhide and noted that between commits 14f9643dc90a and
> 13b937206866 the gaming performance of my computer decreased in two
> times.
> I start bisecting and bisect blame this commit
> 138bcddb86d8a4f842e4ed6f0585abc9b1a764ff.

What do you have on your kernel command line?

What does

grep -r . /sys/devices/system/cpu/vulnerabilities/

say?

Please send a full dmesg, privately is fine too.

If the bisection points to this patch, then it sounds like you have IBPB
enabled as SRSO mitigation which is the heaviest one.

The default one - safe RET - should be a lot better.

> Maybe it is possible to find another approach for solving security
> issue without slowing down?

Yeah, magic. :-)

> If not, then provide an option to turn off this slowdown.

spec_rstack_overflow=off

HTH.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette