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Re: [Xen-devel] Question about the dynamic sizing of the PCI hole

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>

From: Tom Rotenberg <tom.rotenberg@xxxxxxxxx>

Date: Mon, 25 May 2009 12:24:42 +0300

Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>

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And, won't we have any problem if we dynamically size the PCI hole, and not update it in the DSDT we give for the HVM (in the DSDT it's always 0xf0000...)?

2009/5/25 Keir Fraser <keir.fraser@xxxxxxxxxxxxx>

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

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