Re: Question about the dynamic sizing of the PCI hole

[Keir Fraser <keir.fraser@eu.citrix.com>]

On 25/05/2009 10:01, "Tom Rotenberg" <tom.rotenberg@gmail.com> wrote:

> I am reviewing the code of the hvmloader from Xen 3.4, and i saw that in
> changeset 19021, there was a patch which added the ability to dynamically size
> the PCI hole. I have seen that this patch calculates the total memory size,
> but i failed to understand the following lines:
> 
> while ( (mmio_total > (pci_mem_end - pci_mem_start)) &&
>             ((pci_mem_start << 1) != 0) )
>         pci_mem_start <<= 1;
> 
> It looks as if the pci mem start will be increased if there isn't enough space
> for the PCI devices, although, as far as i understand, it should be decreased
> (so the PCI hole will be enlarged). So, shouldn't it be: "pci_mem_start >> =
> 1" ?

Leading bits of this 32-bit value are 1s. Hence left shift is what we want.

 -- Keir