linux-kernel - [RFC PATCH v2 3/4] percpu: Repurpose __percpu tag as a named address space qualifier

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Message-ID: <20240812115945.484051-4-ubizjak@gmail.com>
Date: Mon, 12 Aug 2024 13:57:37 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>,
	Dennis Zhou <dennis@...nel.org>,
	Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux.com>,
	Andy Lutomirski <luto@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Nadav Amit <nadav.amit@...il.com>,
	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Luc Van Oostenryck <luc.vanoostenryck@...il.com>
Subject: [RFC PATCH v2 3/4] percpu: Repurpose __percpu tag as a named address space qualifier

The patch introduces per_cpu_qual define and repurposes __percpu
tag as a named address space qualifier using the new define.

Arches can now conditionally define __per_cpu_qual as their
named address space qualifier for percpu variables.

Signed-off-by: Uros Bizjak <ubizjak@...il.com>
Cc: Dennis Zhou <dennis@...nel.org>
Cc: Tejun Heo <tj@...nel.org>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Nadav Amit <nadav.amit@...il.com>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Luc Van Oostenryck <luc.vanoostenryck@...il.com>
---
 include/asm-generic/percpu.h   | 15 +++++++++++++++
 include/linux/compiler_types.h |  2 +-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h
index c091e09046c5..5f85d7ba8e2d 100644
--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -6,6 +6,21 @@
 #include <linux/threads.h>
 #include <linux/percpu-defs.h>
 
+/*
+ * per_cpu_qual is the qualifier for the percpu named address space.
+ *
+ * Most arches use generic named address space for percpu variables but
+ * some arches define percpu variables in different named address space
+ * (on the x86 arch, percpu variables may be declared as being relative
+ * to the %fs or %gs segments using __seg_fs or __seg_gs named address
+ * space qualifiers).
+ */
+#ifdef __per_cpu_qual
+#define per_cpu_qual __per_cpu_qual
+#else
+#define per_cpu_qual /* nothing */
+#endif
+
 #ifdef CONFIG_SMP
 
 /*
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index f14c275950b5..4c5917b97bc3 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -57,7 +57,7 @@ static inline void __chk_io_ptr(const volatile void __iomem *ptr) { }
 #  define __user	BTF_TYPE_TAG(user)
 # endif
 # define __iomem
-# define __percpu	BTF_TYPE_TAG(percpu)
+# define __percpu	per_cpu_qual BTF_TYPE_TAG(percpu)
 # define __rcu		BTF_TYPE_TAG(rcu)
 
 # define __chk_user_ptr(x)	(void)0
-- 
2.46.0