Re: [PATCH v4 38/40] KVM: arm/arm64: Handle VGICv3 save/restore from the main VGIC code on VHE

From: Marc Zyngier <marc.zyngier@arm.com>
To: Christoffer Dall <christoffer.dall@linaro.org>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Cc: Andrew Jones <drjones@redhat.com>,
	kvm@vger.kernel.org, Tomasz Nowicki <tn@semihalf.com>,
	Julien Grall <julien.grall@arm.com>,
	Yury Norov <ynorov@caviumnetworks.com>,
	Dave Martin <Dave.Martin@arm.com>,
	Shih-Wei Li <shihwei@cs.columbia.edu>
Subject: Re: [PATCH v4 38/40] KVM: arm/arm64: Handle VGICv3 save/restore from the main VGIC code on VHE
Date: Thu, 22 Feb 2018 12:32:11 +0000	[thread overview]
Message-ID: <3de7e88c-e7a2-f9b5-41f7-3b6886459806@arm.com> (raw)
In-Reply-To: <20180215210332.8648-39-christoffer.dall@linaro.org>

On 15/02/18 21:03, Christoffer Dall wrote:
> Just like we can program the GICv2 hypervisor control interface directly
> from the core vgic code, we can do the same for the GICv3 hypervisor
> control interface on VHE systems.
> 
> We do this by simply calling the save/restore functions when we have VHE
> and we can then get rid of the save/restore function calls from the VHE
> world switch function.
> 
> One caveat is that we now write GICv3 system register state before the
> potential early exit path in the run loop, and because we sync back
> state in the early exit path, we have to ensure that we read a
> consistent GIC state from the sync path, even though we have never
> actually run the guest with the newly written GIC state.  We solve this
> by inserting an ISB in the early exit path.
> 
> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
> ---
> 
> Notes:
>     Changes since v2:
>      - Added ISB in the early exit path in the run loop as explained
>        in the commit message.
> 
>  arch/arm64/kvm/hyp/switch.c | 3 ---
>  virt/kvm/arm/arm.c          | 1 +
>  virt/kvm/arm/vgic/vgic.c    | 5 +++++
>  3 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index cbafc27a617b..466cfcdbcaf3 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -399,8 +399,6 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
>  	__activate_traps(vcpu);
>  	__activate_vm(vcpu->kvm);
>  
> -	__vgic_restore_state(vcpu);
> -
>  	sysreg_restore_guest_state_vhe(guest_ctxt);
>  	__debug_switch_to_guest(vcpu);
>  
> @@ -414,7 +412,6 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
>  	fp_enabled = fpsimd_enabled_vhe();
>  
>  	sysreg_save_guest_state_vhe(guest_ctxt);
> -	__vgic_save_state(vcpu);
>  
>  	__deactivate_traps(vcpu);
>  
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index 5bd879c78951..6de7641f3ff2 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -717,6 +717,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  		if (ret <= 0 || need_new_vmid_gen(vcpu->kvm) ||
>  		    kvm_request_pending(vcpu)) {
>  			vcpu->mode = OUTSIDE_GUEST_MODE;
> +			isb(); /* Ensure work in x_flush_hwstate is committed */
>  			kvm_pmu_sync_hwstate(vcpu);
>  			if (static_branch_unlikely(&userspace_irqchip_in_use))
>  				kvm_timer_sync_hwstate(vcpu);
> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> index 12e2a28f437e..d0a19a8c196a 100644
> --- a/virt/kvm/arm/vgic/vgic.c
> +++ b/virt/kvm/arm/vgic/vgic.c
> @@ -19,6 +19,7 @@
>  #include <linux/list_sort.h>
>  #include <linux/interrupt.h>
>  #include <linux/irq.h>
> +#include <asm/kvm_hyp.h>
>  
>  #include "vgic.h"
>  
> @@ -753,6 +754,8 @@ static inline void vgic_save_state(struct kvm_vcpu *vcpu)
>  {
>  	if (!static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif))
>  		vgic_v2_save_state(vcpu);
> +	else if (has_vhe())
> +		__vgic_v3_save_state(vcpu);
>  }
>  
>  /* Sync back the hardware VGIC state into our emulation after a guest's run. */
> @@ -777,6 +780,8 @@ static inline void vgic_restore_state(struct kvm_vcpu *vcpu)
>  {
>  	if (!static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif))
>  		vgic_v2_restore_state(vcpu);
> +	else if (has_vhe())
> +		__vgic_v3_restore_state(vcpu);
>  }
>  
>  /* Flush our emulation state into the GIC hardware before entering the guest. */
> 

I'm slowly wrapping my brain around this thing again. If I grasp the
general idea, we end up with two cases:

(1) The GIC is accessible from the kernel, and we save/restore it
outside of the HYP code.

(2) The GIC is only accessible from the HYP code, and we do it there.

Maybe we should bite the bullet and introduce that primitive instead?

Thanks,

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