Re: User mode Virt -> Phys

Jamie Lokier (lkd@tantalophile.demon.co.uk)
Wed, 13 Jan 1999 12:51:52 +0000


On Wed, Jan 13, 1999 at 03:56:21AM -0500, Mike A. Harris wrote:
> Gee. DMA from userland? Might as well have userland run in ring
> 0 then... unless this is a special case, and not a general
> kernel option suggestion. If someone is going to compromize
> their system like that, they might as well use MSDOS IMHO.

We'd happily use MSDOS if it provided all the services Linux provides...
Like being able to run Linux applications at the same time as the ring 0
stuff, for example. Linux is much more than a mere protection mechanism.

Actually, we do have a specialist network & data processing application
that is far too slow when the network I/O is partitioned between kernel
and user space. At the same time, we use Linux itself to provide a good
ddevelopment/management environment.

Hard to believe, I know, but even handling interrupts is _way_ too slow
(latency) - so we are building special hardware to modify user space
thread scheduling lists directly through bus mastering DMA.

My userdma driver is that, a device driver. So it is not a general
kernel thing and security for normal users will not be compromised.

-- Jamie

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