Re: [Xen-devel] Mapping pci resources for graphics passthrough

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

It¹s that way because a BAR base has to be aligned on a boundary the
power-of-two size of the BAR. Passing thru gfx before may not have worked
because the PCI I/O hole below 4GB was not big enough. That is fixed now in
xen-unstable by dynamically sizing the hole.

 -- Keir


On 22/01/2009 00:29, "Alexia Benington" <alexbenington@xxxxxxxxx> wrote:

> 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.



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