[PATCH v3 06/15] KVM: arm64: Restore mdcr_el2 from vcpu

[Will Deacon]

On Wed, Jul 21, 2021 at 08:37:21AM +0100, Fuad Tabba wrote:
> On Tue, Jul 20, 2021 at 3:53 PM Andrew Jones <drjones at redhat.com> wrote:
> >
> > On Mon, Jul 19, 2021 at 05:03:37PM +0100, Fuad Tabba wrote:
> > > On deactivating traps, restore the value of mdcr_el2 from the
> > > newly created and preserved host value vcpu context, rather than
> > > directly reading the hardware register.
> > >
> > > Up until and including this patch the two values are the same,
> > > i.e., the hardware register and the vcpu one. A future patch will
> > > be changing the value of mdcr_el2 on activating traps, and this
> > > ensures that its value will be restored.
> > >
> > > No functional change intended.
> >
> > I'm probably missing something, but I can't convince myself that the host
> > will end up with the same mdcr_el2 value after deactivating traps after
> > this patch as before. We clearly now restore whatever we had when
> > activating traps (presumably whatever we configured at init_el2_state
> > time), but is that equivalent to what we had before with the masking and
> > ORing that this patch drops?
> 
> You're right. I thought that these were actually being initialized to
> the same values, but having a closer look at the code the mdcr values
> are not the same as pre-patch. I will fix this.

Can you elaborate on the issue here, please? I was just looking at this
but aren't you now relying on __init_el2_debug to configure this, which
should be fine?

Will