Re: [PATCH v8 2/2] x86/sgx: Add an attribute for the amount of SGX memory in a NUMA node

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Oct 18, 2021 at 04:57:44PM +0300, Jarkko Sakkinen wrote:
> The amount of SGX memory on the system is determined by the BIOS and it
> varies wildly between systems.  It can be from dozens of MB's on desktops
> or VM's, up to many GB's on servers.  Just like for regular memory, it is
> sometimes useful to know the amount of usable SGX memory in the system.
> 
> Add an attribute for the amount of SGX memory in bytes to each NUMA
> node. The path is /sys/devices/system/node/node[0-9]*/sgx/size.
> Calculate these values by summing up EPC section sizes for each node
> during the driver initalization.
> 
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> ---
> v8:
> * Fix a bug in sgx_numa_init(): node->dev should be only set after
>   sysfe_create_group().  Otherwise, sysfs_remove_group() will issue a
>   warning in sgx_numa_exit(), when sgx_create_group() is unsuccessful,
>   because the group does not exist.
> 
> v7:
> * Shorten memory_size to size. The prefix makes the name only longer
>   but does not clarify things more than "size" would.
> * Use device_attribute instead of kobj_attribute.
> * Use named attribute group instead of creating raw kobject just for
>   the "sgx" subdirectory.
> 
> v6:
> * Initialize node->size to zero in sgx_setup_epc_section(), when the
>   node is first accessed.
> 
> v5
> * A new patch based on the discussion on
>   https://lore.kernel.org/linux-sgx/3a7cab4115b4f902f3509ad8652e616b91703e1d.camel@kernel.org/T/#t
> ---
>  Documentation/ABI/stable/sysfs-devices-node |  7 ++
>  arch/x86/kernel/cpu/sgx/main.c              | 85 +++++++++++++++++++++
>  arch/x86/kernel/cpu/sgx/sgx.h               |  2 +
>  3 files changed, 94 insertions(+)
> 
> diff --git a/Documentation/ABI/stable/sysfs-devices-node b/Documentation/ABI/stable/sysfs-devices-node
> index 484fc04bcc25..12dc2149e8e0 100644
> --- a/Documentation/ABI/stable/sysfs-devices-node
> +++ b/Documentation/ABI/stable/sysfs-devices-node
> @@ -176,3 +176,10 @@ Contact:	Keith Busch <keith.busch@intel.com>
>  Description:
>  		The cache write policy: 0 for write-back, 1 for write-through,
>  		other or unknown.
> +
> +What:		/sys/devices/system/node/nodeX/sgx/size
> +Date:		October 2021
> +Contact:	Jarkko Sakkinen <jarkko@kernel.org>
> +Description:
> +		Total available physical SGX memory, also known as Enclave Page
> +		Cache (EPC), in bytes.
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index a6e313f1a82d..dc1d46c51323 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -714,9 +714,11 @@ static bool __init sgx_page_cache_init(void)
>  			spin_lock_init(&sgx_numa_nodes[nid].lock);
>  			INIT_LIST_HEAD(&sgx_numa_nodes[nid].free_page_list);
>  			node_set(nid, sgx_numa_mask);
> +			sgx_numa_nodes[nid].size = 0;
>  		}
>  
>  		sgx_epc_sections[i].node =  &sgx_numa_nodes[nid];
> +		sgx_numa_nodes[nid].size += size;
>  
>  		sgx_nr_epc_sections++;
>  	}
> @@ -790,6 +792,81 @@ int sgx_set_attribute(unsigned long *allowed_attributes,
>  }
>  EXPORT_SYMBOL_GPL(sgx_set_attribute);
>  
> +#ifdef CONFIG_NUMA
> +static ssize_t size_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> +	unsigned long size = 0;
> +	int nid;
> +
> +	for (nid = 0; nid < num_possible_nodes(); nid++) {
> +		if (dev == sgx_numa_nodes[nid].dev) {
> +			size = sgx_numa_nodes[nid].size;
> +			break;
> +		}
> +	}
> +
> +	return sysfs_emit(buf, "%lu\n", size);
> +}
> +DEVICE_ATTR_RO(size);
> +
> +static struct attribute *sgx_node_attrs[] = {
> +	&dev_attr_size.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group sgx_node_attr_group = {
> +	.name = "sgx",
> +	.attrs = sgx_node_attrs,
> +};
> +
> +static void sgx_numa_exit(void)
> +{
> +	struct device *dev;
> +	int nid;
> +
> +	for (nid = 0; nid < num_possible_nodes(); nid++) {
> +		dev = &node_devices[nid]->dev;
> +		if (dev)
> +			sysfs_remove_group(&dev->kobj, &sgx_node_attr_group);
> +	}
> +}
> +
> +static bool sgx_numa_init(void)
> +{
> +	struct sgx_numa_node *node;
> +	struct device *dev;
> +	int nid;
> +	int ret;
> +
> +	for (nid = 0; nid < num_possible_nodes(); nid++) {
> +		if (!sgx_numa_nodes[nid].size)
> +			continue;
> +
> +		node = &sgx_numa_nodes[nid];
> +		dev = &node_devices[nid]->dev;
> +
> +		ret = sysfs_create_group(&dev->kobj, &sgx_node_attr_group);

A huge hint, if a driver has to call a sysfs_* call, something is wrong.

Something is wrong here.

Why are you messing around with a kobject?  This is a device, that you
control, you can just set the default attribute group for it and then
the driver core will add and remove the sysfs group at the proper time,
in the proper way.  Right now you are racing userspace and loosing.

Use the default group list, that is what it is there for.

thanks,

greg k-h