Commit 6c1b7521 authored by Christoffer Dall's avatar Christoffer Dall
Browse files

KVM: arm/arm64: Factor out functionality to get vgic mmio requester_vcpu 



We are about to distinguish between userspace accesses and mmio traps
for a number of the mmio handlers.  When the requester vcpu is NULL, it
means we are handling a userspace access.

Factor out the functionality to get the request vcpu into its own
function, mostly so we have a common place to document the semantics of
the return value.

Also take the chance to move the functionality outside of holding a
spinlock and instead explicitly disable and enable preemption.  This
supports PREEMPT_RT kernels as well.

Acked-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Reviewed-by: default avatarAndre Przywara <andre.przywara@arm.com>
Signed-off-by: default avatarChristoffer Dall <christoffer.dall@linaro.org>
parent 5a245750

virt/kvm/arm/vgic/vgic-mmio.c

+28 −16
Original line number Diff line number Diff line
@@ -122,6 +122,27 @@ unsigned long vgic_mmio_read_pending(struct kvm_vcpu *vcpu, 
	return value;

}



/*

 * This function will return the VCPU that performed the MMIO access and

 * trapped from within the VM, and will return NULL if this is a userspace

 * access.

 *

 * We can disable preemption locally around accessing the per-CPU variable,

 * and use the resolved vcpu pointer after enabling preemption again, because

 * even if the current thread is migrated to another CPU, reading the per-CPU

 * value later will give us the same value as we update the per-CPU variable

 * in the preempt notifier handlers.

 */

static struct kvm_vcpu *vgic_get_mmio_requester_vcpu(void)

{

	struct kvm_vcpu *vcpu;



	preempt_disable();

	vcpu = kvm_arm_get_running_vcpu();

	preempt_enable();

	return vcpu;

}



void vgic_mmio_write_spending(struct kvm_vcpu *vcpu,

			      gpa_t addr, unsigned int len,

			      unsigned long val)
@@ -184,24 +205,10 @@ unsigned long vgic_mmio_read_active(struct kvm_vcpu *vcpu, 
static void vgic_mmio_change_active(struct kvm_vcpu *vcpu, struct vgic_irq *irq,

				    bool new_active_state)

{

	struct kvm_vcpu *requester_vcpu;

	unsigned long flags;

	spin_lock_irqsave(&irq->irq_lock, flags);

	struct kvm_vcpu *requester_vcpu = vgic_get_mmio_requester_vcpu();



	/*

	 * The vcpu parameter here can mean multiple things depending on how

	 * this function is called; when handling a trap from the kernel it

	 * depends on the GIC version, and these functions are also called as

	 * part of save/restore from userspace.

	 *

	 * Therefore, we have to figure out the requester in a reliable way.

	 *

	 * When accessing VGIC state from user space, the requester_vcpu is

	 * NULL, which is fine, because we guarantee that no VCPUs are running

	 * when accessing VGIC state from user space so irq->vcpu->cpu is

	 * always -1.

	 */

	requester_vcpu = kvm_arm_get_running_vcpu();

	spin_lock_irqsave(&irq->irq_lock, flags);



	/*

	 * If this virtual IRQ was written into a list register, we
@@ -213,6 +220,11 @@ static void vgic_mmio_change_active(struct kvm_vcpu *vcpu, struct vgic_irq *irq, 
	 * vgic_change_active_prepare)  and still has to sync back this IRQ,

	 * so we release and re-acquire the spin_lock to let the other thread

	 * sync back the IRQ.

	 *

	 * When accessing VGIC state from user space, requester_vcpu is

	 * NULL, which is fine, because we guarantee that no VCPUs are running

	 * when accessing VGIC state from user space so irq->vcpu->cpu is

	 * always -1.

	 */

	while (irq->vcpu && /* IRQ may have state in an LR somewhere */

	       irq->vcpu != requester_vcpu && /* Current thread is not the VCPU thread */

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