Re: [Android-virt] [PATCH RFC v2 3/3] ARM: KVM: Add support for MMU notifiers

[Antonios Motakis <a.motakis@virtualopensystems.com>]

On 02/10/2012 11:22 PM, Marc Zyngier wrote:
> +ENTRY(__kvm_tlb_flush_vmid)
> +	hvc	#0			@ Switch to Hyp mode
> +	push	{r2, r3}
>
> +	ldrd	r2, r3, [r0, #KVM_VTTBR]
> +	mcrr	p15, 6, r2, r3, c2	@ Write VTTBR
> +	isb
> +	mcr     p15, 0, r0, c8, c7, 0	@ TBLIALL
> +	dsb
> +	isb
> +	mov	r2, #0
> +	mov	r3, #0
> +	mcrr	p15, 6, r2, r3, c2	@ Back to VMID #0
> +	isb
> +
> +	pop	{r2, r3}
> +	hvc	#0			@ Back to SVC
> +	mov	pc, lr
> +ENDPROC(__kvm_tlb_flush_vmid)

With the last VMID implementation, you could get the equivalent effect 
of a per-VMID flush, by just getting a new VMID for the current VM. So 
you could do a (kvm->arch.vmid = 0) to force a new VMID when the guest 
reruns, and save the overhead of that flush (you will do a complete 
flush every 255 times instead of a small one every single time).

Best regards,
Antonios