KVM: arm64: vgic-v3: Expose GICR_TYPER.Last for userspace

Commit 23bde34 ("KVM: arm64: vgic-v3: Drop the
reporting of GICR_TYPER.Last for userspace") temporarily fixed
a bug identified when attempting to access the GICR_TYPER
register before the redistributor region setting, but dropped
the support of the LAST bit.

Emulating the GICR_TYPER.Last bit still makes sense for
architecture compliance though. This patch restores its support
(if the redistributor region was set) while keeping the code safe.

We introduce a new helper, vgic_mmio_vcpu_rdist_is_last() which
computes whether a redistributor is the highest one of a series
of redistributor contributor pages.

With this new implementation we do not need to have a uaccess
read accessor anymore.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210405163941.510258-9-eric.auger@redhat.com

arch/arm64/kvm/vgic/vgic-mmio-v3.c

@@ -251,30 +251,35 @@ static void vgic_mmio_write_v3r_ctlr(struct kvm_vcpu *vcpu,
 		vgic_enable_lpis(vcpu);
 }
 
-static unsigned long vgic_mmio_read_v3r_typer(struct kvm_vcpu *vcpu,
-					      gpa_t addr, unsigned int len)
+static bool vgic_mmio_vcpu_rdist_is_last(struct kvm_vcpu *vcpu)
 {
-	unsigned long mpidr = kvm_vcpu_get_mpidr_aff(vcpu);
+	struct vgic_dist *vgic = &vcpu->kvm->arch.vgic;
 	struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
-	struct vgic_redist_region *rdreg = vgic_cpu->rdreg;
-	int target_vcpu_id = vcpu->vcpu_id;
-	gpa_t last_rdist_typer = rdreg->base + GICR_TYPER +
-			(rdreg->free_index - 1) * KVM_VGIC_V3_REDIST_SIZE;
-	u64 value;
+	struct vgic_redist_region *iter, *rdreg = vgic_cpu->rdreg;
 
-	value = (u64)(mpidr & GENMASK(23, 0)) << 32;
-	value |= ((target_vcpu_id & 0xffff) << 8);
+	if (!rdreg)
+		return false;
 
-	if (addr == last_rdist_typer)
-		value |= GICR_TYPER_LAST;
-	if (vgic_has_its(vcpu->kvm))
-		value |= GICR_TYPER_PLPIS;
+	if (vgic_cpu->rdreg_index < rdreg->free_index - 1) {
+		return false;
+	} else if (rdreg->count && vgic_cpu->rdreg_index == (rdreg->count - 1)) {
+		struct list_head *rd_regions = &vgic->rd_regions;
+		gpa_t end = rdreg->base + rdreg->count * KVM_VGIC_V3_REDIST_SIZE;
 
-	return extract_bytes(value, addr & 7, len);
+		/*
+		 * the rdist is the last one of the redist region,
+		 * check whether there is no other contiguous rdist region
+		 */
+		list_for_each_entry(iter, rd_regions, list) {
+			if (iter->base == end && iter->free_index > 0)
+				return false;
+		}
+	}
+	return true;
 }
 
-static unsigned long vgic_uaccess_read_v3r_typer(struct kvm_vcpu *vcpu,
-						 gpa_t addr, unsigned int len)
+static unsigned long vgic_mmio_read_v3r_typer(struct kvm_vcpu *vcpu,
+					      gpa_t addr, unsigned int len)
 {
 	unsigned long mpidr = kvm_vcpu_get_mpidr_aff(vcpu);
 	int target_vcpu_id = vcpu->vcpu_id;
@@ -286,7 +291,9 @@ static unsigned long vgic_uaccess_read_v3r_typer(struct kvm_vcpu *vcpu,
 	if (vgic_has_its(vcpu->kvm))
 		value |= GICR_TYPER_PLPIS;
 
-	/* reporting of the Last bit is not supported for userspace */
+	if (vgic_mmio_vcpu_rdist_is_last(vcpu))
+		value |= GICR_TYPER_LAST;
+
 	return extract_bytes(value, addr & 7, len);
 }
 
@@ -612,7 +619,7 @@ static const struct vgic_register_region vgic_v3_rd_registers[] = {
 		VGIC_ACCESS_32bit),
 	REGISTER_DESC_WITH_LENGTH_UACCESS(GICR_TYPER,
 		vgic_mmio_read_v3r_typer, vgic_mmio_write_wi,
-		vgic_uaccess_read_v3r_typer, vgic_mmio_uaccess_write_wi, 8,
+		NULL, vgic_mmio_uaccess_write_wi, 8,
 		VGIC_ACCESS_64bit | VGIC_ACCESS_32bit),
 	REGISTER_DESC_WITH_LENGTH(GICR_WAKER,
 		vgic_mmio_read_raz, vgic_mmio_write_wi, 4,
@@ -714,6 +721,7 @@ int vgic_register_redist_iodev(struct kvm_vcpu *vcpu)
 		return -EINVAL;
 
 	vgic_cpu->rdreg = rdreg;
+	vgic_cpu->rdreg_index = rdreg->free_index;
 
 	rd_base = rdreg->base + rdreg->free_index * KVM_VGIC_V3_REDIST_SIZE;
 

include/kvm/arm_vgic.h

@@ -322,6 +322,7 @@ struct vgic_cpu {
 	 */
 	struct vgic_io_device	rd_iodev;
 	struct vgic_redist_region *rdreg;
+	u32 rdreg_index;
 
 	/* Contains the attributes and gpa of the LPI pending tables. */
 	u64 pendbaser;