On Wed, Jun 07, 2017 at 10:16:29AM +0100, Marc Zyngier wrote: > On 06/06/17 21:09, Christoffer Dall wrote: > > 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 ? > > That flag is always cleared at EL1, never set. Actually, only EL2 uses > that macro to *set* flags. An alternative would be to do away with the > macro and use the individual flags, like the 32bit side does. > > What do you think? > I don't understand why the A bit is part of SCTLR_ELx_FLAGS then? Is it used as a mask, is that why? In terms of these patches, I think we should apply these, because they solve the problem and do the same thing. Thanks, -Christoffer
