Re: [Xen-devel] [PATCH v7.1 4/4] xen/x86: Allow stubdom access to irq created for msi.

[Jan Beulich <jbeulich@xxxxxxxx>]

On 26.09.2019 06:05, Marek Marczykowski-Górecki  wrote:
> Stubdomains need to be given sufficient privilege over the guest which it
> provides emulation for in order for PCI passthrough to work correctly.
> When a HVM domain try to enable MSI, QEMU in stubdomain calls
> PHYSDEVOP_map_pirq, but later it needs to call XEN_DOMCTL_bind_pt_irq as
> part of xc_domain_update_msi_irq. Give the stubdomain enough permissions
> over the mapped interrupt in order to bind it successfully to it's
> target domain.
> 
> This is not needed for PCI INTx, because IRQ in that case is known
> beforehand and the stubdomain is given permissions over this IRQ by
> libxl__device_pci_add (there's a do_pci_add against the stubdomain).
> 
> create_irq() already grant IRQ access to hardware_domain, with
> assumption the device model lives there.
> Modify create_irq() to take additional parameter, whether to grant
> permissions to the domain creating the IRQ, which may be dom0 or a
> stubdomain. Do this instead of granting access always to
> hardware_domain. Save ID of the domain given permission, to revoke it in
> destroy_irq() - easier and cleaner than replaying logic of create_irq()
> parameter. Use domid instead of actual reference to the domain,
> because it might get destroyed before destroying IRQ (stubdomain is
> destroyed before its target domain). And it is not an issue,
> because IRQ permissions live within domain structure, so destroying
> a domain also implicitly revoke the permission.  Potential domid
> reuse is detected by checking if that domain does have permission
> over the IRQ being destroyed.
> 
> Then, adjust all callers to provide the parameter. In case of Xen
> internal allocations, set it to false, but for domain accessible
> interrupt set it to true.
> 
> Inspired by 
> https://github.com/OpenXT/xenclient-oe/blob/5e0e7304a5a3c75ef01240a1e3673665b2aaf05e/recipes-extended/xen/files/stubdomain-msi-irq-access.patch
>  by Eric Chanudet <chanudete@xxxxxxxxxxxx>.
> 
> Signed-off-by: Simon Gaiser <simon@xxxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
with a couple of cosmetic things addressed, which I'll do while
committing.

Jan

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