linux-kernel - Re: [PATCH] xen: fix multicall debug data referencing

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Message-ID: <1b3e9102-7d1f-43df-b6a0-9da84bc9ec12@oracle.com>
Date: Thu, 18 Jul 2024 17:56:49 -0400
From: boris.ostrovsky@...cle.com
To: Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, xen-devel@...ts.xenproject.org,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] xen: fix multicall debug data referencing


On 7/18/24 2:21 AM, Juergen Gross wrote:
> The recent adding of multicall debug mixed up the referencing of
> the debug data. A __percpu tagged pointer can't be initialized with a
> plain pointer, so use another percpu variable for the pointer and set
> it on each new cpu via a function.
>
> Fixes: 942d917cb92a ("xen: make multicall debug boot time selectable")
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202407151106.5s7Mnfpz-lkp@intel.com/
> Signed-off-by: Juergen Gross <jgross@...e.com>


IIUIC we only need data until SMP is initialized, so setting per-cpu 
pointer just on cpu0 may be sufficient. Not sure where to do this though.

But this works as well.

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>