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

From: Alexander Duyck
Date: Tue Oct 27 2015 - 11:15:39 EST

On 10/27/2015 02:28 AM, ethan zhao wrote:
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

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


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
Set NumVFs to zero after virtfn_max_buses() computes the maximum number of
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)
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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