Subject: Re: [PATCH 09/26] KVM: arm64: vgic-v3: Take cpu_if pointer directly instead of vcpu

From: Marc Zyngier <[email-masked]>
Date: Fri, 8 May 2020 13:20:51 +0100

On Thu, 7 May 2020 17:26:06 +0100
James Morse <[email-masked]> wrote:

Hi James,

> Hi Marc, Christoffer,
> 
> On 22/04/2020 13:00, Marc Zyngier wrote:
> > From: Christoffer Dall <[email-masked]>
> > 
> > If we move the used_lrs field to the version-specific cpu interface
> > structure, the following functions only operate on the struct
> > vgic_v3_cpu_if and not the full vcpu:
> > 
> >   __vgic_v3_save_state
> >   __vgic_v3_restore_state
> >   __vgic_v3_activate_traps
> >   __vgic_v3_deactivate_traps
> >   __vgic_v3_save_aprs
> >   __vgic_v3_restore_aprs
> > 
> > This is going to be very useful for nested virt,   
> 
> ... because you don't need to consider whether the vcpu is running in vEL2?

That's one of the reasons, as vEL2 is still EL1.

But things become really fun when you run a L2 guest, which is an EL1
guest from the PoV of the guest hypervisor (aka L1). At this stage
what you feed to the HW is not the state that could be populated by L0
for L1, but instead what L1 has created for L2 (with a bit of
additional repainting to adjust some of the interrupt numbers).

So we build a shadow cpu_if on the fly and pass it to the normal vgic
handling functions. I told you it was fun! ;-)

> > so move the used_lrs
> > field and change the prototypes and implementations of these functions to
> > take the cpu_if parameter directly.  
> 
> 
> > No functional change.  
> 
> Looks like no change!
> 
> Reviewed-by: James Morse <[email-masked]>

Thanks!

	M.
-- 
Jazz is not dead. It just smells funny...

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