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

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Message-ID: <830677fa-cba8-1339-197e-07b5a0400144@ozlabs.ru>
Date:   Thu, 31 Aug 2017 13:08:31 +1000
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     Bjorn Helgaas <helgaas@...nel.org>
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 31/08/17 05:02, Bjorn Helgaas wrote:
> 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.

I could not identify any issue so far in my test setup - I recreated VFs
several times, run some traffic through them on one of mellanox'es so the
message+backtrace seems to be the only issue for now.


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


This sounds good to me, thanks for updating the commit log.

I'll still try and finish my homework with updating that comment about the
hole in arch/powerpc/platforms/powernv/pci-ioda.c.

Cheers.

> 
> 
> 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");
>  
> 


-- 
Alexey