[RFC PATCH 13/45] KVM: arm/arm64: vgic-new: Export register access interface

[Andre Przywara]

Userland can access the emulated GIC to save and restore its state
for initialization or migration purposes.
The kvm_io_bus API requires an absolute gpa, which does not fit the
KVM_DEV_ARM_VGIC_GRP_DIST_REGS user API, that only provides relative
offsets. So we explicitly iterate our register list to connect
userland to the VGIC.

Signed-off-by: Andre Przywara <andre.przywara at arm.com>
Reviewed-by: Eric Auger <eric.auger at linaro.org>
---
 virt/kvm/arm/vgic/vgic.h      |  2 ++
 virt/kvm/arm/vgic/vgic_mmio.c | 45 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 47 insertions(+)

diff --git a/virt/kvm/arm/vgic/vgic.h b/virt/kvm/arm/vgic/vgic.h
index 53730ba..a462e2b 100644
--- a/virt/kvm/arm/vgic/vgic.h
+++ b/virt/kvm/arm/vgic/vgic.h
@@ -25,6 +25,8 @@ void vgic_v2_process_maintenance(struct kvm_vcpu *vcpu);
 void vgic_v2_fold_lr_state(struct kvm_vcpu *vcpu);
 void vgic_v2_populate_lr(struct kvm_vcpu *vcpu, struct vgic_irq *irq, int lr);
 void vgic_v2_set_underflow(struct kvm_vcpu *vcpu);
+int vgic_v2_dist_access(struct kvm_vcpu *vcpu, bool is_write,
+			int offset, int len, void *val);
 
 #ifdef CONFIG_KVM_ARM_VGIC_V3
 void vgic_v3_irq_change_affinity(struct kvm *kvm, u32 intid, u64 mpidr);
diff --git a/virt/kvm/arm/vgic/vgic_mmio.c b/virt/kvm/arm/vgic/vgic_mmio.c
index 26c46e7..e1fd17f 100644
--- a/virt/kvm/arm/vgic/vgic_mmio.c
+++ b/virt/kvm/arm/vgic/vgic_mmio.c
@@ -113,6 +113,51 @@ struct vgic_register_region vgic_v2_dist_registers[] = {
 		vgic_mmio_read_nyi, vgic_mmio_write_nyi, 16),
 };
 
+/*
+ * Using kvm_io_bus_* to access GIC registers directly from userspace does
+ * not work, since we would need the absolute IPA address of the register
+ * in question, but the userland interface only provides relative offsets.
+ * So we provide our own dispatcher function for that purpose here.
+ */
+static int vgic_mmio_access(struct kvm_vcpu *vcpu,
+			    struct vgic_register_region *region, int nr_regions,
+			    bool is_write, int offset, int len, void *val)
+{
+	int i;
+	struct vgic_io_device dev;
+
+	for (i = 0; i < nr_regions; i++) {
+		int reg_size = region[i].len;
+
+		if (!reg_size)
+			reg_size = (region[i].bits_per_irq * 1024) / 8;
+
+		if ((offset < region[i].reg_offset) ||
+		    (offset + len > region[i].reg_offset + reg_size))
+			continue;
+
+		dev.base_addr	= region[i].reg_offset;
+		dev.redist_vcpu	= vcpu;
+
+		if (is_write)
+			return region[i].ops.write(vcpu, &dev.dev,
+						   offset, len, val);
+		else
+			return region[i].ops.read(vcpu, &dev.dev,
+						  offset, len, val);
+	}
+
+	return -ENODEV;
+}
+
+int vgic_v2_dist_access(struct kvm_vcpu *vcpu, bool is_write,
+			int offset, int len, void *val)
+{
+	return vgic_mmio_access(vcpu, vgic_v2_dist_registers,
+				ARRAY_SIZE(vgic_v2_dist_registers),
+				is_write, offset, len, val);
+}
+
 int kvm_vgic_register_mmio_region(struct kvm *kvm, struct kvm_vcpu *vcpu,
 				  struct vgic_register_region *reg_desc,
 				  struct vgic_io_device *region,
-- 
2.7.3