[RFC PATCH 04/13] arm64: percpu: Factor out percpu offset asm

[Mark Rutland]

Depending on whether the kernel runs at EL1 or EL2, the percpu offset is
stored in either TPIDR_EL1 or TPIDR_EL2, and __kern_my_cpu_offset() uses
an ALTERNATIVE() sequence to read the relevant TPIDR_ELx.

In subsequent patches we'll need to read the percpu offset in other
assembly sequences. Factor the ALTERNATIVE sequence out of
__kern_my_cpu_offset() into a new __KERN_ASM_CPU_OFFSET() macro so that
we can share the code sequence.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Ada Couprie Diaz <ada.coupriediaz@xxxxxxx>
Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
Cc: Marc Zyngier <maz@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Vladimir Murzin <vladimir.murzin@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Yang Shi <yang@xxxxxxxxxxxxxxxxxxxxxx>
---
 arch/arm64/include/asm/percpu.h | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/percpu.h b/arch/arm64/include/asm/percpu.h
index b57b2bb009677..98823c97d534c 100644
--- a/arch/arm64/include/asm/percpu.h
+++ b/arch/arm64/include/asm/percpu.h
@@ -29,6 +29,11 @@ static inline unsigned long __hyp_my_cpu_offset(void)
 	return read_sysreg(tpidr_el2);
 }
 
+#define __KERN_ASM_CPU_OFFSET(dst)					\
+	ALTERNATIVE("mrs " dst ", tpidr_el1",				\
+		    "mrs " dst ", tpidr_el2",				\
+		       ARM64_HAS_VIRT_HOST_EXTN)
+
 static inline unsigned long __kern_my_cpu_offset(void)
 {
 	unsigned long off;
@@ -37,11 +42,11 @@ static inline unsigned long __kern_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(ALTERNATIVE("mrs %0, tpidr_el1",
-			"mrs %0, tpidr_el2",
-			ARM64_HAS_VIRT_HOST_EXTN)
-		: "=r" (off) :
-		"Q" (*(const unsigned long *)current_stack_pointer));
+	asm(
+	__KERN_ASM_CPU_OFFSET("%0")
+	: "=r" (off)
+	: "Q" (*(const unsigned long *)current_stack_pointer)
+	);
 
 	return off;
 }
-- 
2.30.2