Subject: Re: [PATCH v10 3/4] powerpc/powernv: Override pcibios_default_alignment() to force PCI devices to be page aligned

From: Benjamin Herrenschmidt <[email-masked]>
Date: Sat, 15 Apr 2017 07:52:54 +1000

On Fri, 2017-04-14 at 10:58 -0500, Bjorn Helgaas wrote:
> On Mon, Apr 10, 2017 at 07:58:13PM +0800, Yongji Xie wrote:
> > This overrides pcibios_default_alignment() to set default alignment
> > to PAGE_SIZE for all PCI devices on PowerNV platform. Thus sub-page
> > BARs would not share a page and could be mapped into guest when
> > VFIO
> > passthrough them.
> 
> Thanks for doing this.  This looks like a reasonable strategy to me,
> but it would be good to get a powerpc ack for it.

I agree in principle. I'm surprised that PowerPC is the only one
interested here though, what about other platforms who want to use
KVM and PCI pass-through and use Linux to assign BARs ?

Cheers,
Ben.

> > Signed-off-by: Yongji Xie <[email-masked]>
> > ---
> >  arch/powerpc/include/asm/machdep.h        |    2 ++
> >  arch/powerpc/kernel/pci-common.c          |    8 ++++++++
> >  arch/powerpc/platforms/powernv/pci-ioda.c |    7 +++++++
> >  3 files changed, 17 insertions(+)
> > 
> > diff --git a/arch/powerpc/include/asm/machdep.h
> > b/arch/powerpc/include/asm/machdep.h
> > index 5011b69..a82c192 100644
> > --- a/arch/powerpc/include/asm/machdep.h
> > +++ b/arch/powerpc/include/asm/machdep.h
> > @@ -173,6 +173,8 @@ struct machdep_calls {
> >  	/* Called after scan and before resource survey */
> >  	void (*pcibios_fixup_phb)(struct pci_controller *hose);
> >  
> > +	resource_size_t (*pcibios_default_alignment)(struct
> > pci_dev *);
> > +
> >  #ifdef CONFIG_PCI_IOV
> >  	void (*pcibios_fixup_sriov)(struct pci_dev *pdev);
> >  	resource_size_t (*pcibios_iov_resource_alignment)(struct
> > pci_dev *, int resno);
> > diff --git a/arch/powerpc/kernel/pci-common.c
> > b/arch/powerpc/kernel/pci-common.c
> > index ffda24a..ceda574 100644
> > --- a/arch/powerpc/kernel/pci-common.c
> > +++ b/arch/powerpc/kernel/pci-common.c
> > @@ -233,6 +233,14 @@ void pcibios_reset_secondary_bus(struct
> > pci_dev *dev)
> >  	pci_reset_secondary_bus(dev);
> >  }
> >  
> > +resource_size_t pcibios_default_alignment(struct pci_dev *pdev)
> > +{
> > +	if (ppc_md.pcibios_default_alignment)
> > +		return ppc_md.pcibios_default_alignment(pdev);
> > +
> > +	return 0;
> > +}
> > +
> >  #ifdef CONFIG_PCI_IOV
> >  resource_size_t pcibios_iov_resource_alignment(struct pci_dev
> > *pdev, int resno)
> >  {
> > diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c
> > b/arch/powerpc/platforms/powernv/pci-ioda.c
> > index e367382..354c852 100644
> > --- a/arch/powerpc/platforms/powernv/pci-ioda.c
> > +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> > @@ -3297,6 +3297,11 @@ static void pnv_pci_setup_bridge(struct
> > pci_bus *bus, unsigned long type)
> >  	}
> >  }
> >  
> > +static resource_size_t pnv_pci_default_alignment(struct pci_dev
> > *pdev)
> > +{
> > +	return PAGE_SIZE;
> > +}
> > +
> >  #ifdef CONFIG_PCI_IOV
> >  static resource_size_t pnv_pci_iov_resource_alignment(struct
> > pci_dev *pdev,
> >  						      int resno)
> > @@ -3830,6 +3835,8 @@ static void __init
> > pnv_pci_init_ioda_phb(struct device_node *np,
> >  		hose->controller_ops =
> > pnv_pci_ioda_controller_ops;
> >  	}
> >  
> > +	ppc_md.pcibios_default_alignment =
> > pnv_pci_default_alignment;
> > +
> >  #ifdef CONFIG_PCI_IOV
> >  	ppc_md.pcibios_fixup_sriov =
> > pnv_pci_ioda_fixup_iov_resources;
> >  	ppc_md.pcibios_iov_resource_alignment =
> > pnv_pci_iov_resource_alignment;
> > -- 
> > 1.7.9.5
> >