> -----Original Message----- > From: Bjorn Helgaas [mailto:helg...@kernel.org] > Sent: Tuesday, February 16, 2016 2:44 PM > To: Jake Oshins <ja...@microsoft.com> > Cc: bhelg...@google.com; linux-...@vger.kernel.org; > gre...@linuxfoundation.org; KY Srinivasan <k...@microsoft.com>; linux- > ker...@vger.kernel.org; de...@linuxdriverproject.org; o...@aepfle.de; > a...@canonical.com; vkuzn...@redhat.com; t...@linutronix.de; Haiyang > Zhang <haiya...@microsoft.com>; marc.zyng...@arm.com; Hadden > Hoppert <hadd...@microsoft.com> > Subject: Re: [PATCH RESEND v2 3/3] PCI: hv: New paravirtual PCI front-end > for Hyper-V VMs > > On Tue, Feb 16, 2016 at 09:46:55PM +0000, Jake Oshins wrote: > > > -----Original Message----- > > > From: Bjorn Helgaas [mailto:helg...@kernel.org] > > > Sent: Tuesday, February 16, 2016 8:46 AM > > > To: Jake Oshins <ja...@microsoft.com> > > > Cc: bhelg...@google.com; linux-...@vger.kernel.org; > > > gre...@linuxfoundation.org; KY Srinivasan <k...@microsoft.com>; > > > linux- ker...@vger.kernel.org; de...@linuxdriverproject.org; > > > o...@aepfle.de; a...@canonical.com; vkuzn...@redhat.com; > > > t...@linutronix.de; Haiyang Zhang <haiya...@microsoft.com>; > > > marc.zyng...@arm.com; Hadden Hoppert <hadd...@microsoft.com> > > > 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'm not familiar with how Hyper-V works, but I guess you're saying that > Hyper-V controls what the guest sees via _SEG as well as what it sees via the > instance ID. > > Bjorn
Yes, exactly. To the point, the Hyper-V Generation 1 VM (which is an emulation of a 440BX/PIIX4 platform) has one root PCI bus with no _SEG object at all, which implies a value of zero. The Hyper-V Generation 2 VM (which doesn't emulate any existing machine) doesn't have any root PCI bus at all until a device is passed through and this driver is loaded. -- Jake _______________________________________________ devel mailing list de...@linuxdriverproject.org http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
