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Re: [PATCH v3 2/7] PCI: Ignore enforced alignment to VF BARs

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On Fri, Jul 01, 2016 at 01:27:17PM +0800, Yongji Xie wrote:
>>On Thu, Jun 30, 2016 at 06:53:08PM +0800, Yongji Xie wrote:
>>>VF BARs are read-only zeroes according to SRIOV spec,
>>>the normal way(writing BARs) of allocating resources wouldn't
>>>be applied to VFs. The VFs' resources would be allocated
>>>when we enable SR-IOV capability. So we should not try to
>>>reassign alignment after we enable VFs. It's meaningless
>>>and will release the allocated resources which leads to a bug.
>>>
>>>Signed-off-by: Yongji Xie <xyjxie@linux.vnet.ibm.com>
>>>---
>>>drivers/pci/pci.c |    4 ++++
>>>1 file changed, 4 insertions(+)
>>>
>>>diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>>>index be8f72c..6ae02de 100644
>>>--- a/drivers/pci/pci.c
>>>+++ b/drivers/pci/pci.c
>>>@@ -4822,6 +4822,10 @@ void pci_reassigndev_resource_alignment(struct pci_dev *dev)
>>>	resource_size_t align, size;
>>>	u16 command;
>>>
>>>+	/* We should never try to reassign VF's alignment */
>>>+	if (dev->is_virtfn)
>>>+		return;
>>>+
>>Yongji, I think it's correct to ignore VF's BARs. Another concern is:
>>it's safe to apply alignment to PF's IOV BARs? Lets have an extreme
>>example here: one PF has 16 VFs; each VF has only one 1KB. It means
>>the only PF IOV BAR is 16KB. I don't see how it works after expanding
>>it to 64KB which is the page size. It might be not a problem on PowerNV
>>platform, but potentially a issue on x86?
>
>Seems like the alignment would not be applied to IOV BARs because
>pci_reassigndev_resource_alignment() will be called before
>sriov_init().
>

Correct, thanks for the claim. I guess the alignment applied to PF IOV
BARs should be ignored as well? Anyway, the IOV BARs are retireved from
SRIOV capability. It deserves a comment if you plan to take the change.
Actually, the comment here (for ignoring alignment to VF BARs) can be
improved a bit as well, it'd better why the alignment cannot be applied.

Thanks,
Gavin

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[PATCH v3 0/7] PCI: Add support for enforcing all MMIO BARs not to share PAGE_SIZE Yongji Xie <xyjxie@linux.vnet.ibm.com> - 2016-06-30 13:00 +0200
  [PATCH v3 3/7] PCI: Do not disable memory decoding in pci_reassigndev_resource_alignment() Yongji Xie <xyjxie@linux.vnet.ibm.com> - 2016-06-30 13:00 +0200
    Re: [PATCH v3 3/7] PCI: Do not disable memory decoding in  pci_reassigndev_resource_alignment() Gavin Shan <gwshan@linux.vnet.ibm.com> - 2016-07-01 03:00 +0200
      Re: [PATCH v3 3/7] PCI: Do not disable memory decoding in  pci_reassigndev_resource_alignment() Yongji Xie <xyjxie@linux.vnet.ibm.com> - 2016-07-01 10:10 +0200
  [PATCH v3 1/7] PCI: Ignore enforced alignment when kernel uses existing firmware setup Yongji Xie <xyjxie@linux.vnet.ibm.com> - 2016-06-30 13:00 +0200
    Re: [PATCH v3 1/7] PCI: Ignore enforced alignment when kernel uses  existing firmware setup Gavin Shan <gwshan@linux.vnet.ibm.com> - 2016-07-01 02:30 +0200
      Re: [PATCH v3 1/7] PCI: Ignore enforced alignment when kernel uses  existing firmware setup Yongji Xie <xyjxie@linux.vnet.ibm.com> - 2016-07-01 06:50 +0200
  [PATCH v3 2/7] PCI: Ignore enforced alignment to VF BARs Yongji Xie <xyjxie@linux.vnet.ibm.com> - 2016-06-30 13:00 +0200
    Re: [PATCH v3 2/7] PCI: Ignore enforced alignment to VF BARs Gavin Shan <gwshan@linux.vnet.ibm.com> - 2016-07-01 02:50 +0200
      Re: [PATCH v3 2/7] PCI: Ignore enforced alignment to VF BARs Yongji Xie <xyjxie@linux.vnet.ibm.com> - 2016-07-01 07:30 +0200
        Re: [PATCH v3 2/7] PCI: Ignore enforced alignment to VF BARs Gavin Shan <gwshan@linux.vnet.ibm.com> - 2016-07-01 08:10 +0200
          Re: [PATCH v3 2/7] PCI: Ignore enforced alignment to VF BARs Yongji Xie <xyjxie@linux.vnet.ibm.com> - 2016-07-01 08:50 +0200
            Re: [PATCH v3 2/7] PCI: Ignore enforced alignment to VF BARs Gavin Shan <gwshan@linux.vnet.ibm.com> - 2016-07-02 02:40 +0200
  [PATCH v3 7/7] PCI: Add a macro to set default alignment for all PCI devices Yongji Xie <xyjxie@linux.vnet.ibm.com> - 2016-06-30 13:00 +0200
  [PATCH v3 4/7] PCI: Add a new option for resource_alignment to reassign alignment Yongji Xie <xyjxie@linux.vnet.ibm.com> - 2016-06-30 13:00 +0200
    Re: [PATCH v3 4/7] PCI: Add a new option for resource_alignment to  reassign alignment Gavin Shan <gwshan@linux.vnet.ibm.com> - 2016-07-01 05:40 +0200
      Re: [PATCH v3 4/7] PCI: Add a new option for resource_alignment to  reassign alignment Yongji Xie <xyjxie@linux.vnet.ibm.com> - 2016-07-01 09:00 +0200
  [PATCH v3 6/7] PCI: Add support for enforcing all MMIO BARs to be page aligned Yongji Xie <xyjxie@linux.vnet.ibm.com> - 2016-06-30 13:00 +0200
  [PATCH v3 5/7] PCI: Do not use IORESOURCE_STARTALIGN to identify bridge resources Yongji Xie <xyjxie@linux.vnet.ibm.com> - 2016-06-30 13:00 +0200
    Re: [PATCH v3 5/7] PCI: Do not use IORESOURCE_STARTALIGN to identify  bridge resources Gavin Shan <gwshan@linux.vnet.ibm.com> - 2016-07-01 04:40 +0200
      Re: [PATCH v3 5/7] PCI: Do not use IORESOURCE_STARTALIGN to identify  bridge resources Yongji Xie <xyjxie@linux.vnet.ibm.com> - 2016-07-01 09:10 +0200
        Re: [PATCH v3 5/7] PCI: Do not use IORESOURCE_STARTALIGN to identify  bridge resources Gavin Shan <gwshan@linux.vnet.ibm.com> - 2016-07-02 02:40 +0200

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