linux-kernel - [PATCH v5 30/40] x86/resctrl: Describe resctrl's bitmap size assumptions

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Message-Id: <20241004180347.19985-31-james.morse@arm.com>
Date: Fri,  4 Oct 2024 18:03:37 +0000
From: James Morse <james.morse@....com>
To: x86@...nel.org,
	linux-kernel@...r.kernel.org
Cc: Fenghua Yu <fenghua.yu@...el.com>,
	Reinette Chatre <reinette.chatre@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	H Peter Anvin <hpa@...or.com>,
	Babu Moger <Babu.Moger@....com>,
	James Morse <james.morse@....com>,
	shameerali.kolothum.thodi@...wei.com,
	D Scott Phillips OS <scott@...amperecomputing.com>,
	carl@...amperecomputing.com,
	lcherian@...vell.com,
	bobo.shaobowang@...wei.com,
	tan.shaopeng@...itsu.com,
	baolin.wang@...ux.alibaba.com,
	Jamie Iles <quic_jiles@...cinc.com>,
	Xin Hao <xhao@...ux.alibaba.com>,
	peternewman@...gle.com,
	dfustini@...libre.com,
	amitsinght@...vell.com,
	David Hildenbrand <david@...hat.com>,
	Rex Nie <rex.nie@...uarmicro.com>,
	Dave Martin <dave.martin@....com>,
	Shaopeng Tan <tan.shaopeng@...fujitsu.com>
Subject: [PATCH v5 30/40] x86/resctrl: Describe resctrl's bitmap size assumptions

resctrl operates on configuration bitmaps and a bitmap of allocated
CLOSID, both are stored in a u32.

MPAM supports configuration/portion bitmaps and PARTIDs larger
than will fit in a u32.

Add some preprocessor values that make it clear why MPAM clamps
some of these values. This will make it easier to find code related
to these values if this resctrl behaviour ever changes.

Signed-off-by: James Morse <james.morse@....com>
Tested-by: Carl Worth <carl@...amperecomputing.com> # arm64
Tested-by: Shaopeng Tan <tan.shaopeng@...fujitsu.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@...fujitsu.com>
---
 include/linux/resctrl.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index bbce79190b13..7af6c40764ed 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -27,6 +27,17 @@ int proc_resctrl_show(struct seq_file *m,
 /* max value for struct rdt_domain's mbps_val */
 #define MBA_MAX_MBPS   U32_MAX
 
+/*
+ * Resctrl uses a u32 as a closid bitmap. The maximum closid is 32.
+ */
+#define RESCTRL_MAX_CLOSID		32
+
+/*
+ * Resctrl uses u32 to hold the user-space config. The maximum bitmap size is
+ * 32.
+ */
+#define RESCTRL_MAX_CBM			32
+
 /* Walk all possible resources, with variants for only controls or monitors. */
 #define for_each_rdt_resource(_r)						\
 	for ((_r) = resctrl_arch_get_resource(0);				\
-- 
2.39.2