On Fri, Dec 01, 2017 at 01:53:01PM +0000, Mark Rutland wrote: > On Thu, Nov 30, 2017 at 04:39:41PM +0000, Will Deacon wrote: > > .macro kernel_ventry, el, label, regsize = 64 > > .align 7 > > +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0 > > + .if \el == 0 > > + .if \regsize == 64 > > + mrs x30, tpidrro_el0 > > + msr tpidrro_el0, xzr > > + .else > > + mov x30, xzr > > I guess that's just to prevent acccidental leaks if we dump registers > somewhere, since we used x30 as a scratch register?
Indeed. I don't have a concrete example, but I was worried about things like perf and ptrace, which might allow you to get at the AArch64 register state for a compat task so it felt like a good idea to zero this. Will
