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

[Stanislav Kinsburskii]

On Wed, Nov 09, 2022 at 11:07:33AM -0800, Nuno Das Neves wrote:
> 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>
> ---
>  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

Reviewed-by: Stanislav Kinsburskii <skinsburskii@xxxxxxxxxxxxxxxxxxx>