linux-kernel - [PATCH] topology/sysfs: Hide PPIN on systems that do not support it.

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Date:   Wed,  6 Apr 2022 15:01:50 -0700
From:   Tony Luck <tony.luck@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Smita Koralahalli Channabasappa 
        <smita.koralahallichannabasappa@....com>,
        Wei Huang <wei.huang2@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        patches@...ts.linux.dev, Tony Luck <tony.luck@...el.com>
Subject: [PATCH] topology/sysfs: Hide PPIN on systems that do not support it.

Systems that do not support a Protected Processor Identification Number
currently report:

	# cat /sys/devices/system/cpu/cpu0/topology/ppin
	0x0

which is confusing/wrong.

Add a ".is_visible" function to suppress inclusion of the ppin file.

Fixes: ab28e944197f ("topology/sysfs: Add PPIN in sysfs under cpu topology")
Signed-off-by: Tony Luck <tony.luck@...el.com>
---
 drivers/base/topology.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/base/topology.c b/drivers/base/topology.c
index e9d1efcda89b..706dbf8bf249 100644
--- a/drivers/base/topology.c
+++ b/drivers/base/topology.c
@@ -152,9 +152,21 @@ static struct attribute *default_attrs[] = {
 	NULL
 };
 
+static umode_t topology_is_visible(struct kobject *kobj,
+				   struct attribute *attr, int unused)
+{
+	struct device *dev = kobj_to_dev(kobj);
+
+	if (attr == &dev_attr_ppin.attr && !topology_ppin(dev->id))
+		return 0;
+
+	return attr->mode;
+}
+
 static const struct attribute_group topology_attr_group = {
 	.attrs = default_attrs,
 	.bin_attrs = bin_attrs,
+	.is_visible = topology_is_visible,
 	.name = "topology"
 };
 
-- 
2.35.1