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

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Message-ID: <2163ef83-3633-a8cf-3416-0e37a6c500db@ozlabs.ru>
Date:   Fri, 18 Aug 2017 08:05:42 +1000
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     linuxppc-dev@...ts.ozlabs.org, Bjorn Helgaas <bhelgaas@...gle.com>
Cc:     kvm@...r.kernel.org, Yongji Xie <elohimes@...il.com>,
        Eric Auger <eric.auger@...hat.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 11/08/17 18:19, 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/
> 
> Two questions were raised then. I'll try to comment on this below.

Bjorn, ping? Thanks.

> 
>> 1) "res" is already in the resource tree, so we shouldn't be changing
>>   its start address, because that may make the tree inconsistent,
>>   e.g., the resource may no longer be completely contained in its
>>   parent, it may conflict with a sibling, etc.
> 
> We should not, yes. But...
> 
> At the boot time IOV BAR gets as much MMIO space as it can possibly use.
> (Embarassingly I cannot trace where this is coming from, 8GB is selected
> via pci_assign_unassigned_root_bus_resources() path somehow).
> For example, it is 256*32MB=8GB where 256 is maximum PEs number and 32MB
> is a PF/VF BAR size. Whatever shifting we do afterwards, the boudaries of
> that 8GB area do not change and we test it in pnv_pci_vf_resource_shift():
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/platforms/powernv/pci-ioda.c#n987
> 
>> 2) If we update "res->start", shouldn't we update "res->end"
>>   correspondingly?
> 
> We have to update the PF's IOV BAR address as we allocate PEs dynamically
> and we do not know in advance where our VF numbers start in that
> 8GB window. So we change IOV BASR start. Changing the end may make it
> look more like there is a free area to use but in reality it won't be
> usable as well as the area we "release" by shifting the start address.
> 
> We could probably move that M64 MMIO window by the same delta in
> opposite direction so the IOV BAR start address would remain the same
> but its VF#0 would be mapped to let's say PF#5. I am just afraid there
> is an alignment requirement for these M64 window start address; and this
> would be even more tricky to manage.
> 
> We could also create reserved areas for the amount of space "release" by
> moving the start address, not sure how though.
> 
> So how do we proceed with this particular patch now? Thanks.
> ---
>  drivers/pci/iov.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> 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