RE: [PATCH RESEND v2 3/3] PCI: hv: New paravirtual PCI front-end for Hyper-V VMs

[Jake Oshins]

> -----Original Message-----
> From: Bjorn Helgaas [mailto:helgaas@xxxxxxxxxx]
> Sent: Tuesday, February 16, 2016 8:46 AM
> To: Jake Oshins <jakeo@xxxxxxxxxxxxx>
> Cc: bhelgaas@xxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx;
> gregkh@xxxxxxxxxxxxxxxxxxx; KY Srinivasan <kys@xxxxxxxxxxxxx>; linux-
> kernel@xxxxxxxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx;
> apw@xxxxxxxxxxxxx; vkuznets@xxxxxxxxxx; tglx@xxxxxxxxxxxxx; Haiyang
> Zhang <haiyangz@xxxxxxxxxxxxx>; marc.zyngier@xxxxxxx; Hadden
> Hoppert <haddenh@xxxxxxxxxxxxx>
> Subject: Re: [PATCH RESEND v2 3/3] PCI: hv: New paravirtual PCI front-end
> for Hyper-V VMs
> 
> Hi Jake,
> 
> Looks good to me overall; I marked a few nits below.
> 
> The only real question I have is about domain number allocation.  See
> the note below.
> 
[snip]
> > +
> > +	/*
> > +	 * The PCI bus "domain" is what is called "segment" in
> > +	 * ACPI and other specs.  Pull it from the instance ID,
> > +	 * to get something unique.  Bytes 8 and 9 are what is used
> > +	 * in Windows guests, so do the same thing for consistency.
> > +	 */
> > +
> > +	hbus->sysdata.domain = hdev->dev_instance.b[9] |
> > +			       hdev->dev_instance.b[8] << 8;
> 
> How do we know this is unique?  We don't have any idea what the
> platform will put in _SEG, so I think there's a potential conflict
> here.  The Intel VMD driver (arch/x86/pci/vmd.c) has a similar
> problem, and it looks for unused domain numbers starting at 0x10000
> (see vmd_find_free_domain()).
> 

Bjorn, thank you for your very thorough reviews.  I deeply appreciate it.  I checked the Hyper-V code and it currently does guarantee that these values are unique.  When I resend the series, I'll add a comment to that effect.  I'll also add a comment to Hyper-V that says that it has to stay that way.

I'll resend shortly.

Thanks again,
Jake