linux-kernel - [RFC PATCH mpam mpam/snapshot/v6.12-rc1 v4 2/5] arm_mpam: Add limitation for the Narrow-PARTID feature

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Message-ID: <20250104101224.873926-3-zengheng4@huawei.com>
Date: Sat, 4 Jan 2025 18:12:21 +0800
From: Zeng Heng <zengheng4@...wei.com>
To: <Dave.Martin@....com>, <james.morse@....com>
CC: <bobo.shaobowang@...wei.com>, <linux-arm-kernel@...ts.infradead.org>,
	<jonathan.cameron@...wei.com>, <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH mpam mpam/snapshot/v6.12-rc1 v4 2/5] arm_mpam: Add limitation for the Narrow-PARTID feature

Because it needs to support mixed systems that include MSCs with and
without Narrow-PARTID support, there are the following incompatible
control issues.

If an MSC does not support Narrow-PARTID and its control method is not of
the "partition bitmap" type, then delivering the resctrl control group
configuration across multiple PARTIDs will change the user's expected
behavior.

Currently, there is no way to solve this problem by programming different
control values simply, so here decide to restrict the usage scenarios of
this feature. When we find that the MATA MSC does not support the
Narrow-PARTID feature, the driver will disable the feature, which means
get_num_reqpartid() directly returns the number of intPARTIDs.

Signed-off-by: Zeng Heng <zengheng4@...wei.com>
---
 drivers/platform/arm64/mpam/mpam_resctrl.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/platform/arm64/mpam/mpam_resctrl.c b/drivers/platform/arm64/mpam/mpam_resctrl.c
index ac3d228befcf..b9a33001916b 100644
--- a/drivers/platform/arm64/mpam/mpam_resctrl.c
+++ b/drivers/platform/arm64/mpam/mpam_resctrl.c
@@ -168,6 +168,21 @@ u32 resctrl_arch_get_num_closid(struct rdt_resource *ignored)

 static u32 get_num_reqpartid(void)
 {
+	struct mpam_resctrl_res *res;
+	struct rdt_resource *r_mba;
+	struct mpam_props *cprops;
+
+	r_mba = resctrl_arch_get_resource(RDT_RESOURCE_MBA);
+	res = container_of(r_mba, struct mpam_resctrl_res, resctrl_res);
+	cprops = &res->class->props;
+
+	/*
+	 * If the MBA does not support Narrow-PARTID,
+	 * then the feature should be disabled at the system level.
+	 */
+	if (!mpam_has_feature(mpam_feat_partid_nrw, cprops))
+		return resctrl_arch_get_num_closid(NULL);
+
 	return mpam_partid_max + 1;
 }

-- 
2.25.1