[Xen-devel] Root cause of xen bug 1306: Dom0 hangs when destorying one guest with MSI NIC assigned

["Shan, Haitao" <haitao.shan@xxxxxxxxx>]

Hi, Espen,

Some recent changsets break the MSI function. Please see my comments embedded 
in the following code snippet.
Another problem is the following function is invoked by pci_release_devices, 
which is executed before iommu_domain_destroy. However, the following function 
must be executed after unbinding all guest pirqs. The unbinding code is located 
in iommu_domain_destroy.

I am not familiar with recent IOMMU code. Could you please have a look?

static void msi_free_vectors(struct pci_dev* dev)
{
    struct msi_desc *entry, *tmp;
    irq_desc_t *desc;
    unsigned long flags;

retry:
    list_for_each_entry_safe( entry, tmp, &dev->msi_list, list )
    {
        desc = &irq_desc[entry->vector];

    local_irq_save(flags);
    if ( !spin_trylock(&desc->lock) )
    {
        local_irq_restore(flags);
        goto retry;
    }

        spin_lock_irqsave(&desc->lock, flags);
-----→the above line should be removed, otherwise dead lock will occur by 
acquiring a lock already acquired.
        if ( desc->handler == &pci_msi_type )
        {
            /* MSI is not shared, so should be released already */
            BUG_ON(desc->status & IRQ_GUEST);
            desc->handler = &no_irq_type;
        }

        msi_free_vector(entry->vector);
        spin_unlock_irqrestore(&desc->lock, flags);
    }
}

Best Regards
Shan Haitao

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