Xen devel - May 2005 - RE: asterisk, ztdummy, and usb (and HZ = 100 under xen ???)

> On 21 May 2005, at 08:53, James Harper wrote:
> 
> We''re going to rip the fixed ticker out of Xen and allow domains
to
> specify a background ticker at a rate of their choice, which ought to
> fix this for you.
So I could have a domain with 100HZ, and another with 1000HZ? That would
be nice.
> Of course, you''re pretty screwed running this kind of
> thing on Xen unless you dedicate a whole CPU to the relevant domain.
Which would be the clicks and pops I hear :)

I''m only testing VoIP as a proof of concept idea, and have been doing
some coding on kernel stuff, which is where xen is great. Even though
it''s remote I can reboot a crashed domain easily, and have yet to
completely hose the domain by doing something stupid with a pci device
mapped to the domain.

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?

Thanks

James

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel

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


_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel