Re: [Xen-devel] asterisk, ztdummy, and usb (and HZ = 100 under xen ???)

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 22 May 2005, at 03:15, James Harper wrote:

> Just on that subject, under what conditions would a domain with
> permissions to access a pci device be able to bring down the machine if
> I did something stupid in the kernel driver?
Assuming you have restricted the domain to just accessing registers and 
IRQs belonging to the device it controls, I think the only way would be 
by programming the device to wreak havoc on its behalf (by DMAing 
arbitrary memory). It also has control of an interrupt line, so if that 
is shared it might be possible for the domain to arrange an interrupt 
storm that either you mask, affecting servicing of other devices on 
that line, or you end up in interrupt livelock. This could be fixed by 
masking the interrupt, terminating the domain, clearing the enable bits 
in the device's PCI space, then unmasking the interrupt. In any case, 
legacy interrupts are on their way out, replaced with message-based 
interrupts.
 -- Keir


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