Alex Villacís Lasso wrote: > I have a Motorola SM56 PCI Winmodem card for which I want to write a > driver. The card is the one described here: > http://xmodem.org/chipsets/motorola/motorola_sm56pci.html . This card is > also mentioned at > http://www.linuxdriverproject.org/foswiki/bin/view/Main/DriversNeeded as > one of the cards for which Linux drivers are needed but not freely > available. I have tried googling around but I cannot find any reference > to a datasheet that tells me the usage of the hardware registers for > this card. Therefore I want to try the following: > - install a virtual machine package, either QEMU or Bochs > - install an OS for which a SM56 driver is available (I am thinking > Windows 98), and install said SM56 driver. > - modify the virtual machine code to add code to expose a virtual PCI > card with the same resources as the SM56 PCI card. This code will log > the register accesses performed on the virtual SM56, and then pass them > to the actual card. Currently the only resource the card exposes is a > 256-byte MMIO region. > - with the real SM56 plugged in the host, write a userspace driver that > will be contacted by my code in the modified virtual machine, and > perform the actual register accesses as directed by the virtual machine > > However, I am worried about DMA accesses. If the sequence of register > accesses happen to set up a DMA transfer, I might end up writing data > from the card to an arbitrary memory address on the host (which was > supposed to be valid in the guest) and crash my machine. Therefore I ask > the following: > > Is there any measure I can take to guard against the scenario described > above? > Is there an alternative to find out how the card works, besides the > strategy shown above? > Is there any other caveat that I should be aware of? Don't let the card be PCI master so it can't start PCI transfers on it's own. I doubt a modem device will do DMA anyway ...
Attachment:
signature.asc
Description: This is a digitally signed message part.
