[PATCH v2 09/12] ARM: percpu: add SMP_ON_UP support
Ard Biesheuvel
ardb at kernel.org
Tue Nov 30 04:58:58 PST 2021
Permit the use of the TPIDRPRW system register for carrying the per-CPU
offset in generic SMP configurations that also target non-SMP capable
ARMv6 cores. This uses the SMP_ON_UP code patching framework to turn all
TPIDRPRW accesses into reads/writes of entry #0 in the __per_cpu_offset
array.
While at it, switch over some existing direct TPIDRPRW accesses in asm
code to invocations of a new helper that is patched in the same way when
necessary.
Note that CPU_V6+SMP without SMP_ON_UP results in a kernel that does not
boot on v6 CPUs without SMP extensions, so add this dependency to
Kconfig as well.
Acked-by: Linus Walleij <linus.walleij at linaro.org>
Acked-by: Nicolas Pitre <nico at fluxnic.net>
Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
arch/arm/include/asm/assembler.h | 59 +++++++++++++++++++-
arch/arm/include/asm/insn.h | 24 ++++++++
arch/arm/include/asm/percpu.h | 25 ++++++++-
arch/arm/kernel/entry-armv.S | 16 +-----
arch/arm/kernel/sleep.S | 4 +-
arch/arm/mm/Kconfig | 1 +
6 files changed, 107 insertions(+), 22 deletions(-)
diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index 2095638b7140..f9b3dd0e9ef5 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -220,9 +220,7 @@ THUMB( fpreg .req r7 )
.macro reload_current, t1:req, t2:req
#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRURO
- adr_l \t1, __entry_task @ get __entry_task base address
- mrc p15, 0, \t2, c13, c0, 4 @ get per-CPU offset
- ldr \t1, [\t1, \t2] @ load variable
+ ldr_this_cpu \t1, __entry_task, \t1, \t2
mcr p15, 0, \t1, c13, c0, 3 @ store in TPIDRURO
#endif
.endm
@@ -312,6 +310,26 @@ THUMB( fpreg .req r7 )
#define ALT_UP_B(label) b label
#endif
+ /*
+ * this_cpu_offset - load the per-CPU offset of this CPU into
+ * register 'rd'
+ */
+ .macro this_cpu_offset, rd:req
+#ifdef CONFIG_SMP
+ALT_SMP(mrc p15, 0, \rd, c13, c0, 4)
+#ifdef CONFIG_CPU_V6
+ALT_UP_B(.L1_\@)
+.L0_\@:
+ .subsection 1
+.L1_\@: ldr_va \rd, __per_cpu_offset
+ b .L0_\@
+ .previous
+#endif
+#else
+ mov \rd, #0
+#endif
+ .endm
+
/*
* Instruction barrier
*/
@@ -648,6 +666,41 @@ THUMB( orr \reg , \reg , #PSR_T_BIT )
__ldst_va str, \rn, \tmp, \sym, \cond
.endm
+ /*
+ * ldr_this_cpu_armv6 - Load a 32-bit word from the per-CPU variable 'sym',
+ * without using a temp register. Supported in ARM mode
+ * only.
+ */
+ .macro ldr_this_cpu_armv6, rd:req, sym:req
+ this_cpu_offset \rd
+ .globl \sym
+ .reloc .L0_\@, R_ARM_ALU_PC_G0_NC, \sym
+ .reloc .L1_\@, R_ARM_ALU_PC_G1_NC, \sym
+ .reloc .L2_\@, R_ARM_LDR_PC_G2, \sym
+ add \rd, \rd, pc
+.L0_\@: sub \rd, \rd, #4
+.L1_\@: sub \rd, \rd, #0
+.L2_\@: ldr \rd, [\rd, #4]
+ .endm
+
+ /*
+ * ldr_this_cpu - Load a 32-bit word from the per-CPU variable 'sym'
+ * into register 'rd', which may be the stack pointer,
+ * using 't1' and 't2' as general temp registers. These
+ * are permitted to overlap with 'rd' if != sp
+ */
+ .macro ldr_this_cpu, rd:req, sym:req, t1:req, t2:req
+#if __LINUX_ARM_ARCH__ >= 7 || \
+ (defined(MODULE) && defined(CONFIG_ARM_MODULE_PLTS)) || \
+ (defined(CONFIG_LD_IS_LLD) && CONFIG_LLD_VERSION < 140000)
+ this_cpu_offset \t1
+ mov_l \t2, \sym
+ ldr \rd, [\t1, \t2]
+#else
+ ldr_this_cpu_armv6 \rd, \sym
+#endif
+ .endm
+
/*
* rev_l - byte-swap a 32-bit value
*
diff --git a/arch/arm/include/asm/insn.h b/arch/arm/include/asm/insn.h
index 5475cbf9fb6b..a160ed3ea427 100644
--- a/arch/arm/include/asm/insn.h
+++ b/arch/arm/include/asm/insn.h
@@ -2,6 +2,30 @@
#ifndef __ASM_ARM_INSN_H
#define __ASM_ARM_INSN_H
+#include <linux/types.h>
+
+/*
+ * Avoid a literal load by emitting a sequence of ADD/LDR instructions with the
+ * appropriate relocations. The combined sequence has a range of -/+ 256 MiB,
+ * which should be sufficient for the core kernel as well as modules loaded
+ * into the module region. (Not supported by LLD before release 14)
+ */
+#if !(defined(MODULE) && defined(CONFIG_ARM_MODULE_PLTS)) && \
+ !(defined(CONFIG_LD_IS_LLD) && CONFIG_LLD_VERSION < 140000)
+#define LOAD_SYM_ARMV6(reg, sym) \
+ " .globl " #sym " \n\t" \
+ " .reloc 10f, R_ARM_ALU_PC_G0_NC, " #sym " \n\t" \
+ " .reloc 11f, R_ARM_ALU_PC_G1_NC, " #sym " \n\t" \
+ " .reloc 12f, R_ARM_LDR_PC_G2, " #sym " \n\t" \
+ "10: sub " #reg ", pc, #8 \n\t" \
+ "11: sub " #reg ", " #reg ", #4 \n\t" \
+ "12: ldr " #reg ", [" #reg ", #0] \n\t"
+#else
+#define LOAD_SYM_ARMV6(reg, sym) \
+ " ldr " #reg ", =" #sym " \n\t" \
+ " ldr " #reg ", [" #reg "] \n\t"
+#endif
+
static inline unsigned long
arm_gen_nop(void)
{
diff --git a/arch/arm/include/asm/percpu.h b/arch/arm/include/asm/percpu.h
index e2fcb3cfd3de..ff8f0829e041 100644
--- a/arch/arm/include/asm/percpu.h
+++ b/arch/arm/include/asm/percpu.h
@@ -5,15 +5,22 @@
#ifndef _ASM_ARM_PERCPU_H_
#define _ASM_ARM_PERCPU_H_
+#include <asm/insn.h>
+
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)
+#ifdef CONFIG_SMP
+extern unsigned int smp_on_up;
+
static inline void set_my_cpu_offset(unsigned long off)
{
+ if (IS_ENABLED(CONFIG_CPU_V6) && !smp_on_up)
+ return;
+
/* Set TPIDRPRW */
asm volatile("mcr p15, 0, %0, c13, c0, 4" : : "r" (off) : "memory");
}
@@ -27,8 +34,20 @@ static inline unsigned long __my_cpu_offset(void)
* 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));
+ asm("0: mrc p15, 0, %0, c13, c0, 4 \n\t"
+#ifdef CONFIG_CPU_V6
+ "1: \n\t"
+ " .subsection 1 \n\t"
+ "2: " LOAD_SYM_ARMV6(%0, __per_cpu_offset) " \n\t"
+ " b 1b \n\t"
+ " .previous \n\t"
+ " .pushsection \".alt.smp.init\", \"a\" \n\t"
+ " .long 0b - . \n\t"
+ " b . + (2b - 0b) \n\t"
+ " .popsection \n\t"
+#endif
+ : "=r" (off)
+ : "Q" (*(const unsigned long *)current_stack_pointer));
return off;
}
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 7f7ac963445c..43d917f0d9a9 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -35,15 +35,14 @@
.macro irq_handler, from_user:req
mov r0, sp
#ifdef CONFIG_IRQSTACKS
- mov_l r2, irq_stack_ptr @ Take base address
- mrc p15, 0, r3, c13, c0, 4 @ Get CPU offset
#ifdef CONFIG_UNWINDER_ARM
mov fpreg, sp @ Preserve original SP
#else
mov r8, fp @ Preserve original FP
mov r9, sp @ Preserve original SP
#endif
- ldr sp, [r2, r3] @ Load SP from per-CPU var
+ ldr_this_cpu sp, irq_stack_ptr, r2, r3
+
.if \from_user == 0
UNWIND( .setfp fpreg, sp )
@
@@ -876,16 +875,7 @@ __bad_stack:
THUMB( bx pc )
THUMB( nop )
THUMB( .arm )
- mrc p15, 0, ip, c13, c0, 4 @ Get per-CPU offset
-
- .globl overflow_stack_ptr
- .reloc 0f, R_ARM_ALU_PC_G0_NC, overflow_stack_ptr
- .reloc 1f, R_ARM_ALU_PC_G1_NC, overflow_stack_ptr
- .reloc 2f, R_ARM_LDR_PC_G2, overflow_stack_ptr
- add ip, ip, pc
-0: add ip, ip, #-4
-1: add ip, ip, #0
-2: ldr ip, [ip, #4]
+ ldr_this_cpu_armv6 ip, overflow_stack_ptr
str sp, [ip, #-4]! @ Preserve original SP value
mov sp, ip @ Switch to overflow stack
diff --git a/arch/arm/kernel/sleep.S b/arch/arm/kernel/sleep.S
index 803b51e5cba0..f909baf17912 100644
--- a/arch/arm/kernel/sleep.S
+++ b/arch/arm/kernel/sleep.S
@@ -71,9 +71,7 @@ ENTRY(__cpu_suspend)
@ Run the suspend code from the overflow stack so we don't have to rely
@ on vmalloc-to-phys conversions anywhere in the arch suspend code.
@ The original SP value captured in R5 will be restored on the way out.
- mov_l r6, overflow_stack_ptr @ Base pointer
- mrc p15, 0, r7, c13, c0, 4 @ Get per-CPU offset
- ldr sp, [r6, r7] @ Address of this CPU's overflow stack
+ ldr_this_cpu sp, overflow_stack_ptr, r6, r7
#endif
add r4, r4, #12 @ Space for pgd, virt sp, phys resume fn
sub sp, sp, r4 @ allocate CPU state on stack
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 58afba346729..a91ff22c6c2e 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -386,6 +386,7 @@ config CPU_V6
select CPU_PABRT_V6
select CPU_THUMB_CAPABLE
select CPU_TLB_V6 if MMU
+ select SMP_ON_UP if SMP
# ARMv6k
config CPU_V6K
--
2.30.2
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