[PATCH 1/3] arm64: KVM: Move CPU ID reg trap setup off the world switch path

[Dave Martin]

On Wed, Dec 06, 2017 at 11:53:00AM +0100, Christoffer Dall wrote:
> On Tue, Dec 05, 2017 at 12:31:51PM +0000, Dave Martin wrote:
> > On Tue, Dec 05, 2017 at 10:09:15AM +0100, Christoffer Dall wrote:
> > > On Fri, Dec 01, 2017 at 03:19:40PM +0000, Dave Martin wrote:
> > > > The HCR_EL2.TID3 flag needs to be set when trapping guest access to
> > > > the CPU ID registers is required.  However, the decision about
> > > > whether to set this bit does not need to be repeated at every
> > > > switch to the guest.
> > > > 
> > > > Instead, it's sufficient to make this decision once and record the
> > > > outcome.
> > > > 
> > > > This patch moves the decision to vcpu_reset_hcr() and records the
> > > > choice made in vcpu->arch.hcr_el2.  The world switch code can then
> > > > load this directly when switching to the guest without the need for
> > > > conditional logic on the critical path.
> > > > 
> > > > Signed-off-by: Dave Martin <Dave.Martin at arm.com>
> > > > Suggested-by: Christoffer Dall <christoffer.dall at linaro.org>
> > > > Cc: Marc Zyngier <marc.zyngier at arm.com>
> > > 
> > > Reviewed-by: Christoffer Dall <christoffer.dall at linaro.org>
> > > 
> > > > 
> > > > ---
> > > > 
> > > > Note to maintainers: this was discussed on-list [1] prior to the merge
> > > > window, but this patch implementing the agreed decision hasn't been
> > > > posted previously.
> > > > 
> > > > This should be considered a fix for v4.15.
> > > 
> > > It's actually easier for me to apply this for v4.16 and base my VHE
> > > optimization patches on it.
> > 
> > If you're happy for this optimisation to be missing for v4.15, I'm fine
> > with that.
> > 
> > Can I leave it you to pick this up then?
> 
> Yes, I applied it to our queue already.

OK, great, thanks
---Dave