From: Saurabh Singh Sengar <ssengar@linux.microsoft.com>
To: Borislav Petkov <bp@alien8.de>
Cc: ssengar@microsoft.com, mikelley@microsoft.com,
tglx@linutronix.de, mingo@redhat.com,
dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com,
peterz@infradead.org, tim.c.chen@linux.intel.com,
will@kernel.org, song.bao.hua@hisilicon.com,
suravee.suthikulpanit@amd.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/cacheinfo: Don't use cpu_llc_shared_map for !CONFIG_SMP
Date: Thu, 18 Aug 2022 05:29:25 -0700 [thread overview]
Message-ID: <20220818122925.GA8507@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net> (raw)
In-Reply-To: <Yv4pOz01nAkafiwd@zn.tnic>
On Thu, Aug 18, 2022 at 01:57:47PM +0200, Borislav Petkov wrote:
> On Wed, Aug 17, 2022 at 09:52:25PM -0700, Saurabh Singh Sengar wrote:
> > Shall I mention here "Non-SMP AMD processor" instead ?
>
> You should explain what that is.
>
> Is that a CONFIG_SMP=n kernel which you boot on a AMD CPU?
Yes, thats correct.
>
> IOW, how do I reproduce the issue you're describing below, here locally?
Boot latest linux kernel on AMD CPU, having CONGIG_SMP=n.
Once booted execute lscpu (just lscpu without any argument ), this will cause segfault.
Please make a note issue is observed with 2.34 version (default lscpu version with
Ubuntu 20.04.4) of lscpu.
Also, if for the above test we take linux kernel code before below commit,
shared_cpu_map file gets created and lscpu just works fine.
b81dce77ced ("cpumask: Fix invalid uniprocessor mask assumption")
>
> Send dmesg pls.
>
dmesg :
We get only 2 lines of dmesg for this segfault.
Step 1: dmesg -c
Step 2: lscpu
Step 3: dmesg
below is the output of step 3.
Dmesg:
[ 6951.530138] lscpu[99034]: segfault at 0 ip 00005557bc9c35ba sp 00007ffced2681c8 error 4 in lscpu[5557bc9c0000+e000]
[ 6951.530145] Code: 4d 39 c2 76 33 48 c1 e9 06 49 89 c8 4c 8d 2c cd 00 00 00 00 44 89 c9 4f 8b 04 c3 83 e1 3f 4d 0f a3 c8 73 14 4c 8b 02 4d 8b 00 <4f> 8b 04 28 49 d3 e8 41 83 e0 01 44 01 c3 48 89 c1 49 39 c4 74 38
> Also, what is the use case?
>
Explained above, putting here more precise steps:
Step 1: Build linux kernel for AMD processor supporting L3 cache with CONFIG_SMP=n.
Step 2: Boot this kernel.
Step 3: Once in command prompt, enter lscpu
If lspu is version 2.34 like the one I have (default with Ubuntu 20.04.4),
segfault will be observed.
> Why would you even build with SMP off?
This is caught in our testing.
>
> Feel free to explain more verbosely what you're trying to accomplish.
>
> Thx.
>
> --
> Regards/Gruss,
> Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette
Please let me know if any thing is unclear or need more info reproducing the scenario.
- Saurabh
next prev parent reply other threads:[~2022-08-18 12:29 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-10 16:15 [PATCH] x86/cacheinfo: Don't use cpu_llc_shared_map for !CONFIG_SMP Saurabh Sengar
2022-08-12 14:56 ` Michael Kelley (LINUX)
2022-08-17 19:40 ` Borislav Petkov
2022-08-18 4:52 ` Saurabh Singh Sengar
2022-08-18 11:57 ` Borislav Petkov
2022-08-18 12:29 ` Saurabh Singh Sengar [this message]
2022-08-19 17:16 ` Borislav Petkov
2022-08-19 17:46 ` Saurabh Singh Sengar
2022-08-20 8:39 ` [PATCH] x86/cacheinfo: Add a cpu_llc_shared_mask() UP variant Borislav Petkov
2022-09-29 9:04 ` [tip: x86/urgent] " tip-bot2 for Borislav Petkov
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