linux-kernel - [PATCH v4 5/7] ARM: Stop using TPIDRPRW to hold per_cpu

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Message-Id: <20210908190605.419064-6-keithpac@amazon.com>
Date:   Wed,  8 Sep 2021 12:06:03 -0700
From:   Keith Packard <keithpac@...zon.com>
To:     linux-kernel@...r.kernel.org
Cc:     Abbott Liu <liuwenliang@...wei.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Ben Segall <bsegall@...gle.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        bpf@...r.kernel.org, Christoph Lameter <cl@...ux.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dennis Zhou <dennis@...nel.org>, devicetree@...r.kernel.org,
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        Frank Rowand <frowand.list@...il.com>,
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        Joe Perches <joe@...ches.com>,
        John Fastabend <john.fastabend@...il.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Keith Packard <keithpac@...zon.com>,
        KP Singh <kpsingh@...nel.org>, kvm@...r.kernel.org,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
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        Uwe Kleine-König 
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Subject: [PATCH v4 5/7] ARM: Stop using TPIDRPRW to hold per_cpu_offset

We're going to store TPIDRPRW here instead

Signed-off-by: Keith Packard <keithpac@...zon.com>
---
 arch/arm/include/asm/percpu.h | 31 -------------------------------
 arch/arm/kernel/setup.c       |  7 -------
 arch/arm/kernel/smp.c         |  3 ---
 3 files changed, 41 deletions(-)

diff --git a/arch/arm/include/asm/percpu.h b/arch/arm/include/asm/percpu.h
index e2fcb3cfd3de..eeafcd6a3e01 100644
--- a/arch/arm/include/asm/percpu.h
+++ b/arch/arm/include/asm/percpu.h
@@ -7,37 +7,6 @@
 
 register unsigned long current_stack_pointer asm ("sp");
 
-/*
- * Same as asm-generic/percpu.h, except that we store the per cpu offset
- * in the TPIDRPRW. TPIDRPRW only exists on V6K and V7
- */
-#if defined(CONFIG_SMP) && !defined(CONFIG_CPU_V6)
-static inline void set_my_cpu_offset(unsigned long off)
-{
-	/* Set TPIDRPRW */
-	asm volatile("mcr p15, 0, %0, c13, c0, 4" : : "r" (off) : "memory");
-}
-
-static inline unsigned long __my_cpu_offset(void)
-{
-	unsigned long off;
-
-	/*
-	 * Read TPIDRPRW.
-	 * We want to allow caching the value, so avoid using volatile and
-	 * instead use a fake stack read to hazard against barrier().
-	 */
-	asm("mrc p15, 0, %0, c13, c0, 4" : "=r" (off)
-		: "Q" (*(const unsigned long *)current_stack_pointer));
-
-	return off;
-}
-#define __my_cpu_offset __my_cpu_offset()
-#else
-#define set_my_cpu_offset(x)	do {} while(0)
-
-#endif /* CONFIG_SMP */
-
 #include <asm-generic/percpu.h>
 
 #endif /* _ASM_ARM_PERCPU_H_ */
diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index ca0201635fac..d0dc60afe54f 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -590,13 +590,6 @@ void __init smp_setup_processor_id(void)
 	for (i = 1; i < nr_cpu_ids; ++i)
 		cpu_logical_map(i) = i == cpu ? 0 : i;
 
-	/*
-	 * clear __my_cpu_offset on boot CPU to avoid hang caused by
-	 * using percpu variable early, for example, lockdep will
-	 * access percpu variable inside lock_release
-	 */
-	set_my_cpu_offset(0);
-
 	pr_info("Booting Linux on physical CPU 0x%x\n", mpidr);
 }
 
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 5e999f1f1aea..8ccf10b34f08 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -410,8 +410,6 @@ asmlinkage void secondary_start_kernel(unsigned int cpu, struct task_struct *tas
 {
 	struct mm_struct *mm = &init_mm;
 
-	set_my_cpu_offset(per_cpu_offset(cpu));
-
 	secondary_biglittle_init();
 
 	/*
@@ -495,7 +493,6 @@ void __init smp_cpus_done(unsigned int max_cpus)
 
 void __init smp_prepare_boot_cpu(void)
 {
-	set_my_cpu_offset(per_cpu_offset(smp_processor_id()));
 }
 
 void __init smp_prepare_cpus(unsigned int max_cpus)
-- 
2.33.0