arm64: KVM: Preserve RES1 bits in SCTLR_EL2

commit d68c1f7f upstream.

__do_hyp_init has the rather bad habit of ignoring RES1 bits and
writing them back as zero. On a v8.0-8.2 CPU, this doesn't do anything
bad, but may end-up being pretty nasty on future revisions of the
architecture.

Let's preserve those bits so that we don't have to fix this later on.
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@linaro.org>
[bwh: Backported to 3.16:
 - s/ELx/EL2/
 - Adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

arch/arm64/include/asm/kvm_arm.h

@@ -89,6 +89,11 @@
 #define SCTLR_EL2_C	(1 << 2)
 #define SCTLR_EL2_A	(1 << 1)
 #define SCTLR_EL2_M	1
+
+#define SCTLR_EL2_RES1	((1 << 4)  | (1 << 5)  | (1 << 11) | (1 << 16) | \
+			 (1 << 16) | (1 << 18) | (1 << 22) | (1 << 23) | \
+			 (1 << 28) | (1 << 29))
+
 #define SCTLR_EL2_FLAGS	(SCTLR_EL2_M | SCTLR_EL2_A | SCTLR_EL2_C |	\
 			 SCTLR_EL2_SA | SCTLR_EL2_I)
 

arch/arm64/kvm/hyp-init.S

@@ -84,10 +84,12 @@ __do_hyp_init:
 	tlbi	alle2
 	dsb	sy
 
-	mrs	x4, sctlr_el2
-	and	x4, x4, #SCTLR_EL2_EE	// preserve endianness of EL2
-	ldr	x5, =SCTLR_EL2_FLAGS
-	orr	x4, x4, x5
+	/*
+	 * Preserve all the RES1 bits while setting the default flags,
+	 * as well as the EE bit on BE.
+	 */
+	ldr	x4, =(SCTLR_EL2_RES1 | SCTLR_EL2_FLAGS)
+CPU_BE(	orr	x4, x4, #SCTLR_EL2_EE)
 	msr	sctlr_el2, x4
 	isb