linux-kernel - Re: [PATCH v2] pci: fix device presence detection for VFs

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Message-ID: <20221108145300.GA472813@bhelgaas>
Date:   Tue, 8 Nov 2022 08:53:00 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Wei Gong <gongwei833x@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org
Subject: Re: [PATCH v2] pci: fix device presence detection for VFs

On Wed, Oct 26, 2022 at 02:11:21AM -0400, Michael S. Tsirkin wrote:
> virtio uses the same driver for VFs and PFs.  Accordingly,
> pci_device_is_present is used to detect device presence. This function
> isn't currently working properly for VFs since it attempts reading
> device and vendor ID.

> As VFs are present if and only if PF is present,
> just return the value for that device.

VFs are only present when the PF is present *and* the PF has VF Enable
set.  Do you care about the possibility that VF Enable has been
cleared?

> Reported-by: Wei Gong <gongwei833x@...il.com>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
> 
> Wei Gong, thanks for your testing of the RFC!
> As I made a small change, would appreciate re-testing.
> 
> Thanks!
> 
> changes from RFC:
> 	use pci_physfn() wrapper to make the code build without PCI_IOV
> 
> 
>  drivers/pci/pci.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 2127aba3550b..899b3f52e84e 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -6445,8 +6445,13 @@ bool pci_devs_are_dma_aliases(struct pci_dev *dev1, struct pci_dev *dev2)
>  
>  bool pci_device_is_present(struct pci_dev *pdev)
>  {
> +	struct pci_dev *physfn = pci_physfn(pdev);
>  	u32 v;
>  
> +	/* Not a PF? Switch to the PF. */
> +	if (physfn != pdev)
> +		return pci_device_is_present(physfn);
> +
>  	if (pci_dev_is_disconnected(pdev))
>  		return false;
>  	return pci_bus_read_dev_vendor_id(pdev->bus, pdev->devfn, &v, 0);
> -- 
> MST
>