Re: [PATCH v2] iov: restore NumVFs register to 0 before return from virtfn_max_buses()

[Alexander Duyck]

On 10/27/2015 02:28 AM, ethan zhao wrote:
> Alexander,
> On 2015/10/27 13:48, Alexander Duyck wrote:
> > On 10/15/2015 10:16 AM, Bjorn Helgaas wrote:
> > > Hi Ethan,
> > >
> > > On Wed, Sep 16, 2015 at 12:19:53PM +0900, Ethan Zhao wrote:
> > > > After commit 4449f079722c ("PCI: Calculate maximum number of buses
> > > > required for VFs"),the initial value of NumVFs register was left to
> > > > non-zero after sriov_init() and no VFs was enabled in device driver.
> > > > this changed the behaviour of kernel exported by lspci and sysfs etc.
> > > > so this patch restore the NumVFs register to zero after the
> > > > calculation of max_VF_buses was done and before return from
> > > > virtfn_max_buses().
> > > >
> > > > Tested on stable 4.1 and passed building on stable 4.3-rc1
> > > >
> > > > Signed-off-by: Ethan Zhao <ethan.zhao@xxxxxxxxxx>
> > > > Tested-by: Sriharsha Yadagudde <sriharsha.devdas@xxxxxxxxxx>
> > > Can you test the patch below?  I'm trying to avoid touching
> > > PCI_SRIOV_NUM_VF in more than one place, and I think it's OK to set it
> > > and test offset/stride at the end, instead of setting NUM_VF to zero,
> > > testing offset/stride, computing max_bus, then setting NUM_VF to zero
> > > again.
> > >
> > > Bjorn
> > >
> > >
> > > commit 8e20e89658f23b8d16b1e21810e9f63c8625129c
> > > Author: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> > > Date:   Thu Oct 15 11:31:21 2015 -0500
> > >
> > >      PCI: Set SR-IOV NumVFs to zero after enumeration
> > >           The enumeration path should leave NumVFs set to zero. But 
> > > after
> > >      4449f079722c ("PCI: Calculate maximum number of buses required 
> > > for VFs"),
> > >      we call virtfn_max_buses() in the enumeration path, which 
> > > changes NumVFs.
> > >      This NumVFs change is visible via lspci and sysfs until a 
> > > driver enables
> > >      SR-IOV.
> > >           Set NumVFs to zero after virtfn_max_buses() computes the 
> > > maximum number of
> > >      buses.
> > >           Fixes: 4449f079722c ("PCI: Calculate maximum number of 
> > > buses required for VFs")
> > >      Based-on-patch-by: Ethan Zhao <ethan.zhao@xxxxxxxxxx>
> > >      Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> > >
> > > diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> > > index ee0ebff..0202ab0 100644
> > > --- a/drivers/pci/iov.c
> > > +++ b/drivers/pci/iov.c
> > > @@ -384,7 +384,7 @@ static int sriov_init(struct pci_dev *dev, int pos)
> > >       int rc;
> > >       int nres;
> > >       u32 pgsz;
> > > -    u16 ctrl, total, offset, stride;
> > > +    u16 ctrl, total;
> > >       struct pci_sriov *iov;
> > >       struct resource *res;
> > >       struct pci_dev *pdev;
> > > @@ -414,11 +414,6 @@ static int sriov_init(struct pci_dev *dev, int 
> > > pos)
> > >     found:
> > >       pci_write_config_word(dev, pos + PCI_SRIOV_CTRL, ctrl);
> > > -    pci_write_config_word(dev, pos + PCI_SRIOV_NUM_VF, 0);
> > > -    pci_read_config_word(dev, pos + PCI_SRIOV_VF_OFFSET, &offset);
> > > -    pci_read_config_word(dev, pos + PCI_SRIOV_VF_STRIDE, &stride);
> > > -    if (!offset || (total > 1 && !stride))
> > > -        return -EIO;
> > >         pci_read_config_dword(dev, pos + PCI_SRIOV_SUP_PGSIZE, &pgsz);
> > >       i = PAGE_SHIFT > 12 ? PAGE_SHIFT - 12 : 0;
> > > @@ -456,8 +451,6 @@ found:
> > >       iov->nres = nres;
> > >       iov->ctrl = ctrl;
> > >       iov->total_VFs = total;
> > > -    iov->offset = offset;
> > > -    iov->stride = stride;
> > >       iov->pgsz = pgsz;
> > >       iov->self = dev;
> > >       pci_read_config_dword(dev, pos + PCI_SRIOV_CAP, &iov->cap);
> > > @@ -475,6 +468,11 @@ found:
> > >       dev->sriov = iov;
> > >       dev->is_physfn = 1;
> > >       iov->max_VF_buses = virtfn_max_buses(dev);
> > > +    pci_iov_set_numvfs(dev, 0);
> > > +    if (!iov->offset || (total > 1 && !iov->stride)) {
> > > +        rc = -EIO;
> > > +        goto failed;
> > > +    }
> > >         return 0;
> >
> > You might want to reorder this a bit.  The problem is offset and 
> > stride can be 0 if numvfs is 0.  So you should probably test offset 
> > and stride 
>  Yes, the spec says "Note: First VF Offset is unused if NumVFs is 0. 
> If NumVFs is greater than 0, First VF Offset must
> 25 not be zero. "
> > first, and then reset numvfs to 0.
>  Why test it before reset numvfs ?

Because pci_iov_set_numvfs will end up resetting offset and stride based 
on the values when it writes the 0 into numvfs.  As such testing it 
after the reset could give you invalid values since offset and stride 
can be 0 when numvfs is 0.

Actually maybe I will go over this and submit a couple patches myself.  
Looking over things it seems like the code has gotten a bit silly since 
virtfn_max_busses looks like it is iterating over VFs and that doesn't 
make much sense when offset and stride are both positive values so it 
should just be a matter of computing the bus of the last VF.

- Alex
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