Re: [PATCH v4 0/4] KVM: arm64: BUG FIX: Correctly handle zero register transfers

[Andrew Jones <drjones@redhat.com>]

On Mon, Dec 07, 2015 at 03:58:11PM -0600, Andrew Jones wrote:
> On Mon, Dec 07, 2015 at 12:48:12PM +0300, Pavel Fedin wrote:
> >  Hello!
> > 
> > > FYI, I tried writing test cases for this issue with kvm-unit-tests. The
> > > issue didn't reproduce for me. It's quite possible my test cases are
> > > flawed
> > 
> >  Indeed they are, a very little thing fell through again... :)
> >  It's not just SP, it's SP_EL0. And you never initialize it to anything because your code always runs in kernel mode, so it's just
> > zero, so you get your zero.
> >  But if you add a little thing in the beginning of your main():
> > 
> > asm volatile("msr sp_el0, %0" : : "r" (0xDEADC0DE0BADC0DE));
> 
> Ah! Thanks for this. The mmio test does now fail for me too. The sysreg
> test still doesn't fail for me (even though I'm doing the above on the
> vcpu I use for that too). Maybe there's something weird with which reg
> I'm using, and whether or not my attempt to get trapping enabled on it
> is working the way I expected. I'll play with it some more.
>

Must be the trapping thing. I switched to dbgbvr0_el1, which has
trapping enabled on it until it's touched, and was able the reproduce
the xzr issue it.

drew