linux-kernel - Re: [PATCH v2] PCI: IOV: read SRIOV_NUM

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Message-ID: <20151015193116.GE17702@localhost>
Date:	Thu, 15 Oct 2015 14:31:16 -0500
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	Ben Shelton <benjamin.h.shelton@...el.com>
Cc:	bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PCI: IOV: read SRIOV_NUM_VF after enabling ARI

On Thu, Oct 08, 2015 at 10:20:17AM -0500, Ben Shelton wrote:
> For some SR-IOV devices, the number of available virtual functions increases
> after enabling ARI.  Currently, SRIOV_NUM_VF is read and saved off before the
> ARI control bit is enabled in SRIOV_CTRL.  This causes an issue when VFs are
> enabled.
> 
> At device init, SRIOV_INITIAL_VF and SRIOV_NUM_VF are specified to contain the
> number of available VFs for the device.  sriov_enable() does a sanity check
> that SRIOV_INITIAL_VF is not greater than iov->total_VFs, the saved-off value
> of SRIOV_NUM_VF.  Since the value of both SRIOV_INITIAL_VF and SRIOV_NUM_VF has
> increased after enabling the ARI bit, the check fails, and the VFs cannot be
> enabled.
> 
> To fix the issue, write SRIOV_CTRL first, and then read SRIOV_NUM_VF.
> 
> Signed-off-by: Ben Shelton <benjamin.h.shelton@...el.com>

I applied this as follows to pci/virtualization for v4.4, thanks, Ben!

This is on top of a NumVFs-related patch, so the diff looks slightly
different, but I think it's functionally equivalent.


commit 3aa71da412fedaee133b4b6e4be4b801c59d6c91
Author: Ben Shelton <benjamin.h.shelton@...el.com>
Date:   Thu Oct 15 12:35:17 2015 -0500

    PCI: Enable SR-IOV ARI Capable Hierarchy before reading TotalVFs
    
    For some SR-IOV devices, the number of available virtual functions, i.e.,
    TotalVFs, increases after setting the ARI Capable Hierarchy bit in the
    SR-IOV Control register.  This violates the SR-IOV spec, r1.1, sec 3.3.6,
    which says TotalVFs is HwInit, but we don't need TotalVFs before setting
    the ARI Capable bit anyway.
    
    Set the ARI Capable Hierarchy bit (if ARI is enabled in the upstream
    bridge) before reading TotalVFs.
    
    [bhelgaas: changelog]
    Signed-off-by: Ben Shelton <benjamin.h.shelton@...el.com>
    Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>

diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index 0202ab0..f8bfc1d 100644
--- a/drivers/pci/iov.c
+++ b/drivers/pci/iov.c
@@ -399,10 +399,6 @@ static int sriov_init(struct pci_dev *dev, int pos)
 		ssleep(1);
 	}
 
-	pci_read_config_word(dev, pos + PCI_SRIOV_TOTAL_VF, &total);
-	if (!total)
-		return 0;
-
 	ctrl = 0;
 	list_for_each_entry(pdev, &dev->bus->devices, bus_list)
 		if (pdev->is_physfn)
@@ -415,6 +411,10 @@ static int sriov_init(struct pci_dev *dev, int pos)
 found:
 	pci_write_config_word(dev, pos + PCI_SRIOV_CTRL, ctrl);
 
+	pci_read_config_word(dev, pos + PCI_SRIOV_TOTAL_VF, &total);
+	if (!total)
+		return 0;
+
 	pci_read_config_dword(dev, pos + PCI_SRIOV_SUP_PGSIZE, &pgsz);
 	i = PAGE_SHIFT > 12 ? PAGE_SHIFT - 12 : 0;
 	pgsz &= ~((1 << i) - 1);
--
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