KVM: arm/arm64: vgic-new: Add userland access to VGIC dist registers (7d450e28) · Commits · 戴 / test

Userland may want to save and restore the state of the in-kernel VGIC, so we provide the code which takes a userland request and translate that into calls to our MMIO framework. From Christoffer: When accessing the VGIC state from userspace we really don't want a VCPU to be messing with the state at the same time, and the API specifies that we should return -EBUSY if any VCPUs are running. Check and prevent VCPUs from running by grabbing their mutexes, one by one, and error out if we fail. (Note: This could potentially be simplified to just do a simple check and see if any VCPUs are running, and return -EBUSY then, without enforcing the locking throughout the duration of the uaccess, if we think that taking/releasing all these mutexes for every single GIC register access is too heavyweight.) Signed-off-by:

Andre Przywara <andre.przywara@arm.com> Signed-off-by:

Christoffer Dall <christoffer.dall@linaro.org>

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

+54 −1

Original line number	Diff line number	Diff line
		@@ -238,7 +238,60 @@ static int vgic_attr_regs_access(struct kvm_device *dev,
		struct kvm_device_attr *attr,
		u32 *reg, bool is_write)
		{
		return -ENXIO;
		gpa_t addr;
		int cpuid, ret, c;
		struct kvm_vcpu vcpu, tmp_vcpu;
		int vcpu_lock_idx = -1;

		cpuid = (attr->attr & KVM_DEV_ARM_VGIC_CPUID_MASK) >>
		KVM_DEV_ARM_VGIC_CPUID_SHIFT;
		vcpu = kvm_get_vcpu(dev->kvm, cpuid);
		addr = attr->attr & KVM_DEV_ARM_VGIC_OFFSET_MASK;

		mutex_lock(&dev->kvm->lock);

		ret = vgic_init(dev->kvm);
		if (ret)
		goto out;

		if (cpuid >= atomic_read(&dev->kvm->online_vcpus)) {
		ret = -EINVAL;
		goto out;
		}

		/*
		* Any time a vcpu is run, vcpu_load is called which tries to grab the
		* vcpu->mutex. By grabbing the vcpu->mutex of all VCPUs we ensure
		* that no other VCPUs are run and fiddle with the vgic state while we
		* access it.
		*/
		ret = -EBUSY;
		kvm_for_each_vcpu(c, tmp_vcpu, dev->kvm) {
		if (!mutex_trylock(&tmp_vcpu->mutex))
		goto out;
		vcpu_lock_idx = c;
		}

		switch (attr->group) {
		case KVM_DEV_ARM_VGIC_GRP_CPU_REGS:
		ret = -EINVAL;
		break;
		case KVM_DEV_ARM_VGIC_GRP_DIST_REGS:
		ret = vgic_v2_dist_uaccess(vcpu, is_write, addr, reg);
		break;
		default:
		ret = -EINVAL;
		break;
		}

		out:
		for (; vcpu_lock_idx >= 0; vcpu_lock_idx--) {
		tmp_vcpu = kvm_get_vcpu(dev->kvm, vcpu_lock_idx);
		mutex_unlock(&tmp_vcpu->mutex);
		}

		mutex_unlock(&dev->kvm->lock);
		return ret;
		}

		/* V2 ops */

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