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Re: [PATCH v7 7/8] xen/arm: enable dom0 to use PCI devices with pci-passthrough=no


  • To: Mykyta Poturai <Mykyta_Poturai@xxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Tue, 4 Feb 2025 15:31:20 +0100
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  • Cc: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Tue, 04 Feb 2025 14:31:30 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 04.02.2025 14:54, Mykyta Poturai wrote:
> From: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
> 
> Enable the use of IOMMU + PCI in dom0 without having to specify
> "pci-passthrough=yes". We rely on dom0 to initialize the PCI controller
> and perform a PHYSDEVOP_pci_device_add call to add each device to SMMU.
> 
> Enable pci_init() for initializing Xen's internal PCI subsystem, and
> allow PHYSDEVOP_pci_device_add when pci-passthrough is disabled.
> 
> is_pci_passthrough_enabled() is not an Arm-only construct, so remove the
> x86 definition of the function.

I can't see how x86 will continue to build correctly then. There's nowhere
else you introduce a replacement.

> --- a/xen/drivers/pci/physdev.c
> +++ b/xen/drivers/pci/physdev.c
> @@ -19,7 +19,7 @@ ret_t pci_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) 
> arg)
>          struct pci_dev_info pdev_info;
>          nodeid_t node = NUMA_NO_NODE;
>  
> -        if ( !is_pci_passthrough_enabled() )
> +        if ( !is_pci_passthrough_enabled() && !iommu_enabled )
>              return -EOPNOTSUPP;
>  
>          ret = -EFAULT;
> @@ -57,7 +57,7 @@ ret_t pci_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) 
> arg)
>      case PHYSDEVOP_pci_device_remove: {
>          struct physdev_pci_device dev;
>  
> -        if ( !is_pci_passthrough_enabled() )
> +        if ( !is_pci_passthrough_enabled() && !iommu_enabled )
>              return -EOPNOTSUPP;
>  
>          ret = -EFAULT;

This is (potentially) a functional change each on x86, which I don't
think would be correct. "Potentially" because without seeing what the
new is_pci_passthrough_enabled() does this is impossible to determine.

Jan



 


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