[PATCH] iommu/hyper-v: Allow hyperv irq remapping without x2apic

[Nuno Das Neves <nunodasneves@linux.microsoft.com>]

If x2apic is not available, hyperv-iommu skips remapping
irqs. This breaks root partition which always needs irqs
remapped.

Fix this by allowing irq remapping regardless of x2apic,
and change hyperv_enable_irq_remapping() to return
IRQ_REMAP_XAPIC_MODE in case x2apic is missing.

Tested with root and non-root hyperv partitions.

Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
---
 drivers/iommu/Kconfig        | 6 +++---
 drivers/iommu/hyperv-iommu.c | 7 ++++---
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index dc5f7a156ff5..cf7433652db0 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -474,13 +474,13 @@ config QCOM_IOMMU
 	  Support for IOMMU on certain Qualcomm SoCs.
 
 config HYPERV_IOMMU
-	bool "Hyper-V x2APIC IRQ Handling"
+	bool "Hyper-V IRQ Handling"
 	depends on HYPERV && X86
 	select IOMMU_API
 	default HYPERV
 	help
-	  Stub IOMMU driver to handle IRQs as to allow Hyper-V Linux
-	  guests to run with x2APIC mode enabled.
+	  Stub IOMMU driver to handle IRQs to support Hyper-V Linux
+	  guest and root partitions.
 
 config VIRTIO_IOMMU
 	tristate "Virtio IOMMU driver"
diff --git a/drivers/iommu/hyperv-iommu.c b/drivers/iommu/hyperv-iommu.c
index e190bb8c225c..abd1826a9e63 100644
--- a/drivers/iommu/hyperv-iommu.c
+++ b/drivers/iommu/hyperv-iommu.c
@@ -123,8 +123,7 @@ static int __init hyperv_prepare_irq_remapping(void)
 	const struct irq_domain_ops *ops;
 
 	if (!hypervisor_is_type(X86_HYPER_MS_HYPERV) ||
-	    x86_init.hyper.msi_ext_dest_id() ||
-	    !x2apic_supported())
+	    x86_init.hyper.msi_ext_dest_id())
 		return -ENODEV;
 
 	if (hv_root_partition) {
@@ -170,7 +169,9 @@ static int __init hyperv_prepare_irq_remapping(void)
 
 static int __init hyperv_enable_irq_remapping(void)
 {
-	return IRQ_REMAP_X2APIC_MODE;
+	if (x2apic_supported())
+		return IRQ_REMAP_X2APIC_MODE;
+	return IRQ_REMAP_XAPIC_MODE;
 }
 
 struct irq_remap_ops hyperv_irq_remap_ops = {
-- 
2.25.1