Subject: Re: [PATCH 03/43] KVM: arm64: gic-v5: Add resident/non-resident hyp calls

From: Marc Zyngier <[email-masked]>
Date: Tue, 28 Apr 2026 15:28:18 +0100

On Mon, 27 Apr 2026 17:07:03 +0100,
Sascha Bischoff <[email-masked]> wrote:
> 
> So far the KVM GICv5 support has been limited to PPIs. These only go
> as far out as the CPU interface, and have no interaction with the
> host's IRS. Therefore, PPIs can be directly used for guests without
> host IRS involvement. However, in order to support both SPIs and LPIs
> IRS involvement is required.

Please keep this in the cover letter. It isn't required to understand
this patch.

> 
> GICv5 introduces the concept of VPE residency - a VPE can be either
> resident or non-resident. When the VPE is resident, the IRS is allowed
> to select interrupts that target that VPE (or the VM) as the HPPI
> (Highest Priority Pending Interrupt). As the IRS handles both SPIs and
> LPIs, these will only be picked as the IRS's HPPI when a VPE is
> resident.
> 
> A GICv5 VPE is made resident by writing to the ICH_CONTEXTR_EL2 with a
> valid VM and VPE ID, and marking it valid in the process. This informs
> the IRS that a specific VPE is running, and that it can begin HPPI
> selection for that VPE. Making a VPE non-resident (by making the
> ICH_CONTEXTR_EL2 invalid) informs the IRS that the VPE is no longer
> running, and it stops HPPI selection for it.
> 
> This change introduces two new hyp calls - one to make a VPE resident
> and its counterpart to make a VPE non-resident. As part of making a
> VPE resident, the ICH_CONTEXTR_EL2.F bit is checked in order to catch
> faults, at which point the kernel will WARN. If everything is
> configured correctly, this should not happen.
> 
> Signed-off-by: Sascha Bischoff <[email-masked]>
> ---
>  arch/arm64/include/asm/kvm_asm.h   |  2 ++
>  arch/arm64/include/asm/kvm_hyp.h   |  2 ++
>  arch/arm64/kvm/hyp/nvhe/hyp-main.c | 15 +++++++++++++++
>  arch/arm64/kvm/hyp/vgic-v5-sr.c    | 25 +++++++++++++++++++++++++
>  include/kvm/arm_vgic.h             |  3 +++
>  5 files changed, 47 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> index fa033be6141ad..8c69f1f4de534 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -79,6 +79,8 @@ enum __kvm_host_smccc_func {
>  	__KVM_HOST_SMCCC_FUNC___kvm_timer_set_cntvoff,
>  	__KVM_HOST_SMCCC_FUNC___vgic_v3_save_aprs,
>  	__KVM_HOST_SMCCC_FUNC___vgic_v3_restore_vmcr_aprs,
> +	__KVM_HOST_SMCCC_FUNC___vgic_v5_make_resident,
> +	__KVM_HOST_SMCCC_FUNC___vgic_v5_make_non_resident,
>  	__KVM_HOST_SMCCC_FUNC___vgic_v5_save_apr,
>  	__KVM_HOST_SMCCC_FUNC___vgic_v5_restore_vmcr_apr,
>  
> diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
> index 8d06b62e7188c..5f9184276b04e 100644
> --- a/arch/arm64/include/asm/kvm_hyp.h
> +++ b/arch/arm64/include/asm/kvm_hyp.h
> @@ -88,6 +88,8 @@ void __vgic_v3_restore_vmcr_aprs(struct vgic_v3_cpu_if *cpu_if);
>  int __vgic_v3_perform_cpuif_access(struct kvm_vcpu *vcpu);
>  
>  /* GICv5 */
> +void __vgic_v5_make_resident(struct vgic_v5_cpu_if *cpu_if);
> +void __vgic_v5_make_non_resident(struct vgic_v5_cpu_if *cpu_if);
>  void __vgic_v5_save_apr(struct vgic_v5_cpu_if *cpu_if);
>  void __vgic_v5_restore_vmcr_apr(struct vgic_v5_cpu_if *cpu_if);
>  /* No hypercalls for the following */
> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> index 9e44c05cf780e..804a9ffdc8594 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> @@ -672,6 +672,19 @@ static void handle___tracing_write_event(struct kvm_cpu_context *host_ctxt)
>  	trace_selftest(id);
>  }
>  
> +static void handle___vgic_v5_make_resident(struct kvm_cpu_context *host_ctxt)
> +{
> +	DECLARE_REG(struct vgic_v5_cpu_if *, cpu_if, host_ctxt, 1);
> +
> +	__vgic_v5_make_resident(kern_hyp_va(cpu_if));
> +}
> +static void handle___vgic_v5_make_non_resident(struct kvm_cpu_context *host_ctxt)
> +{
> +	DECLARE_REG(struct vgic_v5_cpu_if *, cpu_if, host_ctxt, 1);
> +
> +	__vgic_v5_make_non_resident(kern_hyp_va(cpu_if));
> +}
> +
>  static void handle___vgic_v5_save_apr(struct kvm_cpu_context *host_ctxt)
>  {
>  	DECLARE_REG(struct vgic_v5_cpu_if *, cpu_if, host_ctxt, 1);
> @@ -711,6 +724,8 @@ static const hcall_t host_hcall[] = {
>  	HANDLE_FUNC(__kvm_timer_set_cntvoff),
>  	HANDLE_FUNC(__vgic_v3_save_aprs),
>  	HANDLE_FUNC(__vgic_v3_restore_vmcr_aprs),
> +	HANDLE_FUNC(__vgic_v5_make_resident),
> +	HANDLE_FUNC(__vgic_v5_make_non_resident),
>  	HANDLE_FUNC(__vgic_v5_save_apr),
>  	HANDLE_FUNC(__vgic_v5_restore_vmcr_apr),
>  
> diff --git a/arch/arm64/kvm/hyp/vgic-v5-sr.c b/arch/arm64/kvm/hyp/vgic-v5-sr.c
> index 6d69dfe89a96c..04c5846b9abac 100644
> --- a/arch/arm64/kvm/hyp/vgic-v5-sr.c
> +++ b/arch/arm64/kvm/hyp/vgic-v5-sr.c
> @@ -7,6 +7,31 @@
>  
>  #include <asm/kvm_hyp.h>
>  
> +void __vgic_v5_make_resident(struct vgic_v5_cpu_if *cpu_if)
> +{
> +	write_sysreg_s(cpu_if->vgic_contextr, SYS_ICH_CONTEXTR_EL2);
> +	isb();
> +
> +	/* Catch any faults */
> +	cpu_if->vgic_contextr = read_sysreg_s(SYS_ICH_CONTEXTR_EL2);
> +	if (WARN_ON(FIELD_GET(ICH_CONTEXTR_EL2_F, cpu_if->vgic_contextr)))
> +		return;

I don't think this is particularly useful here. With non-VHE, this
results in a panic. If there is a problem, you need to fail the vcpu
entry early, and let the caller find out.

> +
> +	cpu_if->gicv5_vpe.resident = true;
> +}
> +
> +void __vgic_v5_make_non_resident(struct vgic_v5_cpu_if *cpu_if)
> +{
> +	/*
> +	 * Make as non-resident before actually making non-resident. Avoids race
> +	 * with doorbell arriving.
> +	 */
> +	cpu_if->gicv5_vpe.resident = false;

Stores and sysreg accesses are not ordered without a DSB ST in between.

> +
> +	write_sysreg_s(cpu_if->vgic_contextr, SYS_ICH_CONTEXTR_EL2);

Is this really making anything non-resident? Who clears the V bit?

> +	isb();
> +}
> +
>  void __vgic_v5_save_apr(struct vgic_v5_cpu_if *cpu_if)
>  {
>  	cpu_if->vgic_apr = read_sysreg_s(SYS_ICH_APR_EL2);
> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> index fe49fb56dc3c9..d14cf4771d606 100644
> --- a/include/kvm/arm_vgic.h
> +++ b/include/kvm/arm_vgic.h
> @@ -495,6 +495,9 @@ struct vgic_v5_cpu_if {
>  	 */
>  	u64	vgic_icsr;
>  
> +	/* The contextr used to make VPEs resident and non-resident */
> +	u64	vgic_contextr;
> +
>  	struct gicv5_vpe gicv5_vpe;
>  };
>  

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.