Re: [PATCH v3 2/7] PCI: Ignore enforced alignment to VF BARs

[Yongji Xie]

Hi Gavin,

On 2016/7/1 8:39, Gavin Shan wrote:

> On Thu, Jun 30, 2016 at 06:53:08PM +0800, Yongji Xie wrote:
> > VF BARs are read-only zeroes according to SRIOV spec,
> > the normal way(writing BARs) of allocating resources wouldn't
> > be applied to VFs. The VFs' resources would be allocated
> > when we enable SR-IOV capability. So we should not try to
> > reassign alignment after we enable VFs. It's meaningless
> > and will release the allocated resources which leads to a bug.
> >
> > Signed-off-by: Yongji Xie <xyjxie@xxxxxxxxxxxxxxxxxx>
> > ---
> > drivers/pci/pci.c |    4 ++++
> > 1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index be8f72c..6ae02de 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -4822,6 +4822,10 @@ void pci_reassigndev_resource_alignment(struct pci_dev *dev)
> > 	resource_size_t align, size;
> > 	u16 command;
> >
> > +	/* We should never try to reassign VF's alignment */
> > +	if (dev->is_virtfn)
> > +		return;
> > +
> Yongji, I think it's correct to ignore VF's BARs. Another concern is:
> it's safe to apply alignment to PF's IOV BARs? Lets have an extreme
> example here: one PF has 16 VFs; each VF has only one 1KB. It means
> the only PF IOV BAR is 16KB. I don't see how it works after expanding
> it to 64KB which is the page size. It might be not a problem on PowerNV
> platform, but potentially a issue on x86?

Seems like the alignment would not be applied to IOV BARs because
pci_reassigndev_resource_alignment() will be called before
sriov_init().

Thanks,
Yongji