From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keir Fraser <keir.fraser@eu.citrix.com>
Subject: Re: Question about the dynamic sizing of the PCI hole
Date: Mon, 25 May 2009 10:14:14 +0100
Message-ID: <C6401FF6.BB9B%keir.fraser@eu.citrix.com>
References: <8686c3cd0905250201u5eb546a5n35b7600e4b264feb@mail.gmail.com>
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To: Tom Rotenberg <tom.rotenberg@gmail.com>, "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>
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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 siz=
e,
> but i failed to understand the following lines:
>=20
> while ( (mmio_total > (pci_mem_end - pci_mem_start)) &&
> =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 ((pci_mem_start << 1) !=3D 0) )
> =A0=A0=A0=A0=A0=A0=A0 pci_mem_start <<=3D 1;
>=20
> 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 decre=
ased
> (so the PCI hole will be enlarged). So, shouldn't it be: "pci_mem_start >=
> =3D
> 1" ?

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

 -- Keir