arm64: Disable EL2 traps for BRBE instructions executed in EL1

This disables EL2 traps for BRBE instructions executed in EL1. This would
enable BRBE to be configured and used successfully in the guest kernel.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>

arch/arm64/include/asm/el2_setup.h

@@ -161,6 +161,16 @@
 	msr_s	SYS_HFGWTR_EL2, x0
 	msr_s	SYS_HFGITR_EL2, xzr
 
+	mrs	x1, id_aa64dfr0_el1
+	ubfx	x1, x1, #ID_AA64DFR0_EL1_BRBE_SHIFT, #4
+	cbz	x1, .Lskip_brbe_\@
+
+	mov	x0, xzr
+	orr	x0, x0, #HFGITR_EL2_nBRBIALL
+	orr	x0, x0, #HFGITR_EL2_nBRBINJ
+	msr_s	SYS_HFGITR_EL2, x0
+
+.Lskip_brbe_\@:
 	mrs	x1, id_aa64pfr0_el1		// AMU traps UNDEF without AMU
 	ubfx	x1, x1, #ID_AA64PFR0_EL1_AMU_SHIFT, #4
 	cbz	x1, .Lskip_fgt_\@