[PATCH 2/3] arm64: KVM: Allow unaligned accesses at EL2
Christoffer Dall
cdall at linaro.org
Tue Jun 6 13:09:12 PDT 2017
On Tue, Jun 06, 2017 at 07:08:34PM +0100, Marc Zyngier wrote:
> 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.
Why do we set the A flag via SCTLR_ELx_FLAGS in the first place, only to
drop that flag later on for both EL1 and EL2 ?
>
> Cc: stable at vger.kernel.org
> Reported-by: Alexander Graf <agraf at suse.de>
> Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
> ---
> arch/arm64/kvm/hyp-init.S | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
> index 4072d408a4b4..3f9615582377 100644
> --- a/arch/arm64/kvm/hyp-init.S
> +++ b/arch/arm64/kvm/hyp-init.S
> @@ -108,9 +108,10 @@ __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
> --
> 2.11.0
>
Otherwise this looks fine to me.
Thanks,
-Christoffer
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