linux-kernel - Re: [PATCH] x86/MCE, xen/mcelog: Make /dev/mcelog registration messages more precise

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Date:   Wed, 21 Jun 2017 10:56:48 +0800
From:   Ethan Zhao <ethan.kernel@...il.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Tony Luck <tony.luck@...el.com>,
        linux-edac <linux-edac@...r.kernel.org>,
        "<xen-devel@...ts.xenproject.org>" <xen-devel@...ts.xenproject.org>
Subject: Re: [PATCH] x86/MCE, xen/mcelog: Make /dev/mcelog registration
 messages more precise

Borislav,

    How about skipping the misc_register() steps and keep silence if
you know it is running as Dom0 ? as it is easy to know.


Reviewed-by: Ethan Zhao <ethan.zhao@...cle.com>

On Wed, Jun 21, 2017 at 5:16 AM, Borislav Petkov <bp@...en8.de> wrote:
> From: Juergen Gross <jgross@...e.com>
>
> When running under Xen as dom0, /dev/mcelog is being provided by Xen
> instead of the normal mcelog character device of the MCE core. Convert
> an error message being issued by the MCE core in this case to an
> informative message that Xen has registered the device.
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> Cc: Tony Luck <tony.luck@...el.com>
> Cc: linux-edac <linux-edac@...r.kernel.org>
> Cc: x86-ml <x86@...nel.org>
> Cc: xen-devel@...ts.xenproject.org
> Link: http://lkml.kernel.org/r/20170614084059.19294-1-jgross@suse.com
> [ Massage a bit. ]
> Signed-off-by: Borislav Petkov <bp@...e.de>
> ---
>  arch/x86/kernel/cpu/mcheck/dev-mcelog.c | 8 +++++++-
>  drivers/xen/mcelog.c                    | 2 ++
>  2 files changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/mcheck/dev-mcelog.c b/arch/x86/kernel/cpu/mcheck/dev-mcelog.c
> index a80427c30c93..10cec43aac38 100644
> --- a/arch/x86/kernel/cpu/mcheck/dev-mcelog.c
> +++ b/arch/x86/kernel/cpu/mcheck/dev-mcelog.c
> @@ -415,9 +415,15 @@ static __init int dev_mcelog_init_device(void)
>         /* register character device /dev/mcelog */
>         err = misc_register(&mce_chrdev_device);
>         if (err) {
> -               pr_err("Unable to init device /dev/mcelog (rc: %d)\n", err);
> +               if (err == -EBUSY)
> +                       /* Xen dom0 might have registered the device already. */
> +                       pr_info("Unable to init device /dev/mcelog, already registered");
> +               else
> +                       pr_err("Unable to init device /dev/mcelog (rc: %d)\n", err);
> +
>                 return err;
>         }
> +
>         mce_register_decode_chain(&dev_mcelog_nb);
>         return 0;
>  }
> diff --git a/drivers/xen/mcelog.c b/drivers/xen/mcelog.c
> index a493c7315e94..6cc1c15bcd84 100644
> --- a/drivers/xen/mcelog.c
> +++ b/drivers/xen/mcelog.c
> @@ -408,6 +408,8 @@ static int __init xen_late_init_mcelog(void)
>         if (ret)
>                 goto deregister;
>
> +       pr_info("/dev/mcelog registered by Xen\n");
> +
>         return 0;
>
>  deregister:
> --
> 2.13.0
>