HYP Kernel boot requirements

[Catalin Marinas]

On Mon, Nov 25, 2013 at 07:44:08PM +0000, Santosh Shilimkar wrote:
> On Monday 25 November 2013 12:28 PM, Catalin Marinas wrote:
> > On Mon, Nov 25, 2013 at 04:59:16PM +0000, Santosh Shilimkar wrote:
> >> What I am saying is the platforms like OMAP5 already support PM in
> >> mainline kernel and we can't break that for KVM. Boot-loaders
> >> would be thrashed after boot so you need something which runs
> >> in Kernel or along with Kernel to have equivalent of hyp
> >> switching.
> >>
> >> Am not challenging the agreed direction but we need to solve the
> >> PM problem as well before making "all CPU runs boot-loader for
> >> HYP kernels" as a must have. At least its is a change in boot
> >> strategy from existing kernels.
> > 
> > Of course I recommend PSCI which covers both hotplug and suspend ;), but
> > I guess it's not the case for OMAP5. Since OMAP has its own secondary
> > booting protocol and CPU hotplug re-entry, can you not just use
> > different entry point when the primary CPU was initially started in Hyp
> > mode (e.g. omap5_hyp_secondary_startup)?
> > 
> How will that solve the guest secondary boot failure case when using
> the same kernel binary for guest-boot ? Even for primary CPU which
> will be suspended it needs to resume already in HYP mode and its not
> going to go through boot-loader. So the low power code needs to have
> HYP switch code so that CPU resumes in HYP mode.

Is it late to rewrite the OMAP5 firmware?

What I meant is that you have the same kernel binary but with two sets
of entry points, or maybe a single set of entry points and some global
variable that you set during cold boot if the primary CPU is entered in
Hyp mode. So you change the boot loader to switch to Hyp before it
starts the kernel and leave the additional switching to be done by the
secondary entry points (or PM code) based on the variable you set during
cold boot. But I would recommend rewriting the firmware.

> I will look at PSCI more closely and see what can be done here.

PSCI has a different secondary start-up and hotplug/suspend protocol and
CPUs wake up in Hyp if available. But this requires changing your
firmware, PSCI is not a kernel-only thing. Do you need to support both
older and newer kernels with the OMAP5 firmware (and possibly same DT)?

-- 
Catalin