Re: [PATCH v6 12/19] vfio-user: IOMMU support for remote device

[Stefan Hajnoczi]

On Thu, Feb 17, 2022 at 02:48:59AM -0500, Jagannathan Raman wrote:
> +struct RemoteIommuElem {
> +    AddressSpace  as;
> +    MemoryRegion  mr;
> +};
> +
> +GHashTable *remote_iommu_elem_by_bdf;

A mutable global hash table requires synchronization when device
emulation runs in multiple threads.

I suggest using pci_setup_iommu()'s iommu_opaque argument to avoid the
global. If there is only 1 device per remote PCI bus, then there are no
further synchronization concerns.

> +
> +#define INT2VOIDP(i) (void *)(uintptr_t)(i)
> +
> +static AddressSpace *remote_iommu_find_add_as(PCIBus *pci_bus,
> +                                              void *opaque, int devfn)
> +{
> +    struct RemoteIommuElem *elem = NULL;
> +    int pci_bdf = PCI_BUILD_BDF(pci_bus_num(pci_bus), devfn);
> +
> +    if (!remote_iommu_elem_by_bdf) {
> +        return &address_space_memory;
> +    }

When can this happen? remote_configure_iommu() allocates
remote_iommu_elem_by_bdf so it should always be non-NULL.

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