Subject: Re: [PATCH v6 03/39] KVM: arm64: Return early from kvm_finalize_sys_regs() if guest has run

From: Jonathan Cameron <[email-masked]>
Date: Thu, 19 Mar 2026 10:12:29 +0000

On Tue, 17 Mar 2026 11:40:44 +0000
Sascha Bischoff <[email-masked]> wrote:

> If the guest has already run, we have no business finalizing the
> system register state - it is too late. Therefore, check early and
> bail if the VM has already run.
Given it isn't in the scope below, might be worth calling out that
this is skipping kvm_init_nv_sysregs()  So on non NV setups isn't
changing anything but on those it's indeed skipping setup of system
registers.

Seems correct to me, but is this a fix?  So should it have a fixes tag?

> 
> Signed-off-by: Sascha Bischoff <[email-masked]>
> ---
>  arch/arm64/kvm/sys_regs.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 0acd10e50aaba..42c84b7900ff5 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -5659,11 +5659,14 @@ int kvm_finalize_sys_regs(struct kvm_vcpu *vcpu)
>  
>  	guard(mutex)(&kvm->arch.config_lock);
>  
> +	if (kvm_vm_has_ran_once(kvm))
> +		return 0;
> +
>  	/*
>  	 * This hacks into the ID registers, so only perform it when the
>  	 * first vcpu runs, or the kvm_set_vm_id_reg() helper will scream.
>  	 */
> -	if (!irqchip_in_kernel(kvm) && !kvm_vm_has_ran_once(kvm)) {
> +	if (!irqchip_in_kernel(kvm)) {
>  		u64 val;
>  
>  		val = kvm_read_vm_id_reg(kvm, SYS_ID_AA64PFR0_EL1) & ~ID_AA64PFR0_EL1_GIC;