[PATCH 3.16 159/233] arm64: KVM: Allow unaligned accesses at EL2

From: Ben Hutchings
Date: Sat Sep 09 2017 - 19:08:33 EST

3.16.48-rc1 review patch. If anyone has any objections, please let me know.


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

Reported-by: Alexander Graf <agraf@xxxxxxx>
Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
Signed-off-by: Christoffer Dall <cdall@xxxxxxxxxx>
[bwh: Backported to 3.16: s/ELx/EL2/]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
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
@@ -86,9 +86,10 @@ __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_EL2_FLAGS)
+ ldr x4, =(SCTLR_EL2_RES1 | (SCTLR_EL2_FLAGS & ~SCTLR_EL2_A))
CPU_BE( orr x4, x4, #SCTLR_EL2_EE)
msr sctlr_el2, x4