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 <stable@xxxxxxxxxxxxxxx> know about it. >From 78fd6dcf11468a5a131b8365580d0c613bcc02cb Mon Sep 17 00:00:00 2001 From: Marc Zyngier <marc.zyngier@xxxxxxx> Date: Tue, 6 Jun 2017 19:08:34 +0100 Subject: arm64: KVM: Allow unaligned accesses at EL2 From: Marc Zyngier <marc.zyngier@xxxxxxx> 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. Reported-by: Alexander Graf <agraf@xxxxxxx> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx> Signed-off-by: Christoffer Dall <cdall@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/arm64/kvm/hyp-init.S | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/arch/arm64/kvm/hyp-init.S +++ b/arch/arm64/kvm/hyp-init.S @@ -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 marc.zyngier@xxxxxxx 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