From: Nuno Das Neves <nunodasneves@xxxxxxxxxxxxxxxxxxx> Sent: Thursday, November 17, 2022 12:12 PM
>
> 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@xxxxxxxxxxxxxxxxxxx>
> ---
> arch/x86/kernel/cpu/mshyperv.c | 6 ++++++
> drivers/iommu/Kconfig | 6 +++---
> drivers/iommu/hyperv-iommu.c | 11 ++++++++---
> 3 files changed, 17 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 831613959a92..46668e255421 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -475,6 +475,12 @@ static bool __init ms_hyperv_x2apic_available(void)
> * (logically) generates MSIs directly to the system APIC irq domain.
> * There is no HPET, and PCI MSI/MSI-X interrupts are remapped by the
> * pci-hyperv host bridge.
> + *
> + * Note: for a Hyper-V root partition, this will always return false.
> + * The hypervisor doesn't expose these HYPERV_CPUID_VIRT_STACK_* cpuids by
> + * default, they are implemented as intercepts by the Windows Hyper-V stack.
> + * Even a nested root partition (L2 root) will not get them because the
> + * nested (L1) hypervisor filters them out.
> */
> static bool __init ms_hyperv_msi_ext_dest_id(void)
> {
> 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..8302db7f783e 100644
> --- a/drivers/iommu/hyperv-iommu.c
> +++ b/drivers/iommu/hyperv-iommu.c
> @@ -122,9 +122,12 @@ static int __init hyperv_prepare_irq_remapping(void)
> const char *name;
> const struct irq_domain_ops *ops;
>
> + /*
> + * For a Hyper-V root partition, ms_hyperv_msi_ext_dest_id()
> + * will always return false.
> + */
> 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 +173,9 @@ 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
Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
