Patch "arm64: KVM: Allow unaligned accesses at 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: Allow unaligned accesses at 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-allow-unaligned-accesses-at-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 19:08:34 +0100
Subject: arm64: KVM: Allow unaligned accesses at EL2

From: Marc Zyngier <[email protected]>

commit 78fd6dcf11468a5a131b8365580d0c613bcc02cb upstream.

We currently have the SCTLR_EL2.A bit set, trapping unaligned accesses at EL2, but we're not really prepared to deal with it. So far, this has been unnoticed, until GCC 7 started emitting those (in particular 64bit writes on a 32bit boundary).

Since the rest of the kernel is pretty happy about that, let's follow its example and set SCTLR_EL2.A to zero. Modern CPUs don't really care.

---
 arch/arm64/kvm/hyp-init.S |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

@@ -104,9 +104,10 @@ __do_hyp_init:
 
 	/*
 	 * Preserve all the RES1 bits while setting the default flags,
-	 * as well as the EE bit on BE.
+	 * as well as the EE bit on BE. Drop the A flag since the compiler
+	 * is allowed to generate unaligned accesses.
 	 */
-	ldr	x4, =(SCTLR_EL2_RES1 | SCTLR_ELx_FLAGS)
+	ldr	x4, =(SCTLR_EL2_RES1 | (SCTLR_ELx_FLAGS & ~SCTLR_ELx_A))
 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