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

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Date:   Sun, 13 Aug 2023 14:17:25 +0500
From:   Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
To:     Borislav Petkov <bp@...en8.de>
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 1:24 PM Borislav Petkov <bp@...en8.de> wrote:
>
> What do you have on your kernel command line?

log_buf_len=16M sysrq_always_enabled=1 nmi_watchdog=1
amdgpu.lockup_timeout=-1,-1,-1,-1 amdgpu.aspm=0
crashkernel=1G-4G:192M,4G-64G:256M,64G-:512M

> What does
>
> grep -r . /sys/devices/system/cpu/vulnerabilities/
>
> say?

Attached as [vulnerabilities.txt]

>
> Please send a full dmesg, privately is fine too.
>

Attached as [dmesg.zip]

> 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

Thanks, I checked this and it works!

-- 
Best Regards,
Mike Gavrilov.

View attachment "vulnerabilities.txt" of type "text/plain" (1073 bytes)

Download attachment "dmesg.zip" of type "application/zip" (49382 bytes)