linux-kernel - Re: [PATCH v13 2/2] x86/sgx: Add an attribute for the amount of SGX memory in a NUMA node

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Date:   Thu, 6 Jan 2022 21:18:32 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>, reinette.chatre@...el.com,
        linux-kernel@...r.kernel.org, linux-sgx@...r.kernel.org
Subject: Re: [PATCH v13 2/2] x86/sgx: Add an attribute for the amount of SGX
 memory in a NUMA node

On Sat, Jan 01, 2022 at 08:54:51PM -0800, Dave Hansen wrote:
> On 12/28/21 3:45 PM, Jarkko Sakkinen wrote:
> >> If I can provide any further information or testing, let me know!
> > Dave, when is the fix going to be applied [*]?
> > 
> >> Cheers,
> >> Nathan
> > [*] https://lore.kernel.org/linux-sgx/YcGTePmWDMOQU1pn@iki.fi/T/#m831a01bdde347f9e0af2c973986fae0499718201
> 
> Greg preferred hiding the file as opposed to faking a number in there.
> Any testing of the attached would be appreciated.

> 
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> Nathan Chancellor reported an oops when aceessing the
> 'sgx_total_bytes' sysfs file:
> 
> 	https://lore.kernel.org/all/YbzhBrimHGGpddDM@archlinux-ax161/
> 
> The sysfs output code accesses the sgx_numa_nodes[] array
> unconditionally.  However, this array is allocated during SGX
> initialization, which only occurs on systems where SGX is
> supported.
> 
> If the sysfs file is accessed on systems without SGX support,
> sgx_numa_nodes[] is NULL and an oops occurs.
> 
> To fix this, hide the entire nodeX/x86/ attribute group on
> systems without SGX support using the ->is_visible attribute
> group callback.
> 
> Fixes: 50468e431335 ("x86/sgx: Add an attribute for the amount of SGX memory in a NUMA node")
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Jarkko Sakkinen <jarkko@...nel.org>
> Cc: linux-sgx@...r.kernel.org
> Cc: x86@...nel.org
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> ---
> 
>  b/arch/x86/kernel/cpu/sgx/main.c |   11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff -puN arch/x86/kernel/cpu/sgx/main.c~sgx-null-ptr arch/x86/kernel/cpu/sgx/main.c
> --- a/arch/x86/kernel/cpu/sgx/main.c~sgx-null-ptr	2021-12-20 07:56:38.309584807 -0800
> +++ b/arch/x86/kernel/cpu/sgx/main.c	2021-12-20 08:17:28.997705149 -0800
> @@ -910,6 +910,16 @@ static ssize_t sgx_total_bytes_show(stru
>  }
>  static DEVICE_ATTR_RO(sgx_total_bytes);
>  
> +static umode_t arch_node_attr_is_visible(struct kobject * kobj,
> +		struct attribute * attr, int idx)
> +{
> +	/* Make all x86/ attributes invisible when SGX is not initialized: */
> +	if (nodes_empty(sgx_numa_mask))
> +		return 0;
> +
> +	return attr->mode;
> +}
> +
>  static struct attribute *arch_node_dev_attrs[] = {
>  	&dev_attr_sgx_total_bytes.attr,
>  	NULL,
> @@ -918,6 +928,7 @@ static struct attribute *arch_node_dev_a
>  const struct attribute_group arch_node_dev_group = {
>  	.name = "x86",
>  	.attrs = arch_node_dev_attrs,
> +	.is_visible = arch_node_attr_is_visible,
>  };
>  #endif /* CONFIG_NUMA */
>  
> _

I'm compiling now kernel with this applied, reporting soon but the fix
looks good to me.

/Jarkko