linux-kernel - Re: [PATCH kernel] PCI: Disable IOV before pcibios_sriov

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Message-ID: <20170830190206.GU8154@bhelgaas-glaptop.roam.corp.google.com>
Date:   Wed, 30 Aug 2017 14:02:06 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Alexey Kardashevskiy <aik@...abs.ru>
Cc:     linuxppc-dev@...ts.ozlabs.org, kvm@...r.kernel.org,
        Yongji Xie <elohimes@...il.com>,
        Eric Auger <eric.auger@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        shan.gavin@...il.com,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Gavin Shan <gwshan@...ux.vnet.ibm.com>
Subject: Re: [PATCH kernel] PCI: Disable IOV before pcibios_sriov_disable()

On Fri, Aug 11, 2017 at 06:19:33PM +1000, Alexey Kardashevskiy wrote:
> From: Gavin Shan <gwshan@...ux.vnet.ibm.com>
> 
> The PowerNV platform is the only user of pcibios_sriov_disable().
> The IOV BAR could be shifted by pci_iov_update_resource(). The
> warning message in the function is printed if the IOV capability
> is in enabled (PCI_SRIOV_CTRL_VFE && PCI_SRIOV_CTRL_MSE) state.
> 
> This is the backtrace of what is happening:
>    pci_disable_sriov
>    sriov_disable
>    pnv_pci_sriov_disable
>    pnv_pci_vf_resource_shift
>    pci_update_resource
>    pci_iov_update_resource
> 
> This fixes the issue by disabling IOV capability before calling
> pcibios_sriov_disable(). With it, the disabling path matches
> the enabling path: pcibios_sriov_enable() is called before the
> IOV capability is enabled.
> 
> Cc: shan.gavin@...il.com
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Reported-by: Carol L Soto <clsoto@...ibm.com>
> Signed-off-by: Gavin Shan <gwshan@...ux.vnet.ibm.com>
> Tested-by: Carol L Soto <clsoto@...ibm.com>
> Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>
> ---
> 
> This is repost. Since Gavin left the team, I am trying to push it out.
> The previos converstion is here: https://patchwork.ozlabs.org/patch/732653/

I gave up on the previous issue.  I think this patch makes sense as-is
at least as far as the fact that we can't update a struct resource
while the device is still consuming it.  I reworked the changelog to
emphasize that.

I assume the fact that pci_iov_update_resource() dropped the resource
update caused some user-visible issue later on, and I might mention
that, too, if I knew what it was.

Here's what I would consider putting on pci/virtualization (the diff
is unchanged from your post):


commit 08132e7759b3929bea0ccdf8afe81ebf05351389
Author: Gavin Shan <gwshan@...ux.vnet.ibm.com>
Date:   Fri Aug 11 18:19:33 2017 +1000

    PCI: Disable VF decoding before updating resources in pcibios_sriov_disable()
    
    A struct resource represents the address space consumed by a device.  We
    should not modify that resource while the device is actively using the
    address space.  For VFs, pci_iov_update_resource() enforces this by
    printing a warning and doing nothing if the VFE (VF Enable) and MSE (VF
    Memory Space Enable) bits are set.
    
    Previously, both sriov_enable() and sriov_disable() called the
    pcibios_sriov_disable() arch hook, which may update the struct resource,
    while VFE and MSE were enabled.  This effectively dropped the resource
    update pcibios_sriov_disable() intended to do.
    
    Disable VF memory decoding before calling pcibios_sriov_disable().
    
    Reported-by: Carol L Soto <clsoto@...ibm.com>
    Tested-by: Carol L Soto <clsoto@...ibm.com>
    Signed-off-by: Gavin Shan <gwshan@...ux.vnet.ibm.com>
    Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>
    [bhelgaas: changelog]
    Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
    Cc: shan.gavin@...il.com
    Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
    Cc: Paul Mackerras <paulus@...ba.org>

diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index 120485d6f352..ac41c8be9200 100644
--- a/drivers/pci/iov.c
+++ b/drivers/pci/iov.c
@@ -331,7 +331,6 @@ static int sriov_enable(struct pci_dev *dev, int nr_virtfn)
 	while (i--)
 		pci_iov_remove_virtfn(dev, i, 0);
 
-	pcibios_sriov_disable(dev);
 err_pcibios:
 	iov->ctrl &= ~(PCI_SRIOV_CTRL_VFE | PCI_SRIOV_CTRL_MSE);
 	pci_cfg_access_lock(dev);
@@ -339,6 +338,8 @@ static int sriov_enable(struct pci_dev *dev, int nr_virtfn)
 	ssleep(1);
 	pci_cfg_access_unlock(dev);
 
+	pcibios_sriov_disable(dev);
+
 	if (iov->link != dev->devfn)
 		sysfs_remove_link(&dev->dev.kobj, "dep_link");
 
@@ -357,14 +358,14 @@ static void sriov_disable(struct pci_dev *dev)
 	for (i = 0; i < iov->num_VFs; i++)
 		pci_iov_remove_virtfn(dev, i, 0);
 
-	pcibios_sriov_disable(dev);
-
 	iov->ctrl &= ~(PCI_SRIOV_CTRL_VFE | PCI_SRIOV_CTRL_MSE);
 	pci_cfg_access_lock(dev);
 	pci_write_config_word(dev, iov->pos + PCI_SRIOV_CTRL, iov->ctrl);
 	ssleep(1);
 	pci_cfg_access_unlock(dev);
 
+	pcibios_sriov_disable(dev);
+
 	if (iov->link != dev->devfn)
 		sysfs_remove_link(&dev->dev.kobj, "dep_link");