Patch "arm64: KVM: Preserve RES1 bits in SCTLR_EL2" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

arm64: KVM: Preserve RES1 bits in SCTLR_EL2

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     arm64-kvm-preserve-res1-bits-in-sctlr_el2.patch

and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Marc Zyngier <[email protected]>
Date: Tue, 6 Jun 2017 19:08:33 +0100
Subject: arm64: KVM: Preserve RES1 bits in SCTLR_EL2

From: Marc Zyngier <[email protected]>

commit d68c1f7fd1b7148dab5fe658321d511998969f2d 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.

---
 arch/arm64/include/asm/sysreg.h |    4 ++++
 arch/arm64/kvm/hyp-init.S       |   10 ++++++----
 2 files changed, 10 insertions(+), 4 deletions(-)

@@ -94,6 +94,10 @@
 #define SCTLR_ELx_A	(1 << 1)
 #define SCTLR_ELx_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_ELx_FLAGS	(SCTLR_ELx_M | SCTLR_ELx_A | SCTLR_ELx_C | \
 			 SCTLR_ELx_SA | SCTLR_ELx_I)
 

@@ -102,10 +102,12 @@ __do_hyp_init:
 	tlbi	alle2
 	dsb	sy
 
-	mrs	x4, sctlr_el2
-	and	x4, x4, #SCTLR_ELx_EE	// preserve endianness of EL2
-	ldr	x5, =SCTLR_ELx_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_ELx_FLAGS)
+CPU_BE(	orr	x4, x4, #SCTLR_ELx_EE)
 	msr	sctlr_el2, x4
 	isb
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/arm64-kvm-allow-unaligned-accesses-at-el2.patch queue-4.9/arm-kvm-allow-unaligned-accesses-at-hyp.patch queue-4.9/arm64-kvm-preserve-res1-bits-in-sctlr_el2.patch