[RFC PATCH] arch: ARM64: add isb before enable pan

[Huangzhaoyang]

From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>

set_pstate_pan failure is observed in an ARM64 system occasionaly on a reboot
test, which can be work around by a msleep on the sw context. We assume
suspicious on disorder of previous instr of disabling SW_PAN and add an isb here.

PS:
The bootup test failed with a invalid TTBR1_EL1 that equals 0x34000000, which is
alike racing between on chip PAN and SW_PAN.

Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
---
 arch/arm64/kernel/cpufeature.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index efed283..3c0de0d 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1663,6 +1663,7 @@ static void cpu_enable_pan(const struct arm64_cpu_capabilities *__unused)
 	WARN_ON_ONCE(in_interrupt());
 
 	sysreg_clear_set(sctlr_el1, SCTLR_EL1_SPAN, 0);
+	isb();
 	set_pstate_pan(1);
 }
 #endif /* CONFIG_ARM64_PAN */
-- 
1.9.1