[Xen-devel] Mapping pci resources for graphics passthrough

[Alexia Benington <alexbenington@xxxxxxxxx>]

Hi all,

I've been trying to understand the pci_setup function in hvmloader.c in Xen unstable. I'm kinda lost at Line 328.
base = (resource->base + bar_sz - 1) & ~(bar_sz - 1)

I'd appreciate if someone could explain to me why base is calculated this way. Specifically, I don't understand the bitwise AND with the one's complements of "bar_sz-1".

The reason why I'm doing this is that I'm hoping to modify hvmloader such that it can map the correct memory for a PCI-e video card. I've been able to passthrough the video card to a HVM guest. However, the OS (tried Linux, Vista or XP) is not able to load the driver correctly, although lspci (on Linux) does show that the video card has been passed through. I suspect it is because the video RAM and ROM has not been mapped as required, thus the video BIOS cannot be loaded. I would like to try out with only one guest first, just to see if it works and leaving out the complexities of multiplexing the graphics card with several guests. It is also fine if dom0 loses control of the graphics card. I can use serial.

Thanks and have a nice day!

Cheers,
Alex
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