[PATCH 4/5] KVM: arm64: Prevent re-finalisation of pKVM for a given CPU

[Quentin Perret]

On Thursday 23 Sep 2021 at 12:22:55 (+0100), Will Deacon wrote:
> __pkvm_prot_finalize() completes the deprivilege of the host when pKVM
> is in use by installing a stage-2 translation table for the calling CPU.
> 
> Issuing the hypercall multiple times for a given CPU makes little sense,
> but in such a case just return early with -EPERM rather than go through
> the whole page-table dance again.
> 
> Cc: Marc Zyngier <maz at kernel.org>
> Cc: Quentin Perret <qperret at google.com>
> Signed-off-by: Will Deacon <will at kernel.org>
> ---
>  arch/arm64/kvm/hyp/nvhe/mem_protect.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> index bacd493a4eac..cafe17e5fa8f 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> @@ -123,6 +123,9 @@ int __pkvm_prot_finalize(void)
>  	struct kvm_s2_mmu *mmu = &host_kvm.arch.mmu;
>  	struct kvm_nvhe_init_params *params = this_cpu_ptr(&kvm_init_params);
>  
> +	if (params->hcr_el2 & HCR_VM)
> +		return -EPERM;

And you check this rather than the static key because we flip it upfront
I guess. Makes sense to me, but maybe a little comment would be useful :)
In any case:

Reviewed-by: Quentin Perret <qperret at google.com>

Thanks,
Quentin