arm64: dbm: Invalidate local TLB when setting TCR_EL1.HD

TCR_EL1.HD is permitted to be cached in a TLB, so invalidate the local
TLB after setting the bit when detected support for the feature. Although
this isn't strictly necessary, since we can happily operate with the bit
effectively clear, the current code uses an ISB in a half-hearted attempt
to make the change effective, so let's just fix that up.

Link: https://lore.kernel.org/r/20201001110405.18617-1-will@kernel.org
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/cpufeature.c

@@ -1443,6 +1443,7 @@ static inline void __cpu_enable_hw_dbm(void)
 
 	write_sysreg(tcr, tcr_el1);
 	isb();
+	local_flush_tlb_all();
 }
 
 static bool cpu_has_broken_dbm(void)