linux-kernel - Re: [PATCH] vfio/pci: Add extra test for extended capabilities

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Message-ID: <jpgwqclx4yw.fsf@nelium.bos.redhat.com>
Date:	Thu, 12 Jun 2014 16:12:07 -0400
From:	Bandan Das <bsd@...hat.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] vfio/pci: Add extra test for extended capabilities

Alex Williamson <alex.williamson@...hat.com> writes:

> If the PCI core set cfg_size isn't large enough for extended
> capabilities, then they're not there.  Extended config space may be
> inaccessible due to a PCI bridge, in which case cfg_size may be cut
> short.

Just curious, is this part of the spec or just a convention ? I mean
could there be devices with quirks ?

> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> ---
>  drivers/vfio/pci/vfio_pci_config.c |   13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
> index 83cd157..4a62a37 100644
> --- a/drivers/vfio/pci/vfio_pci_config.c
> +++ b/drivers/vfio/pci/vfio_pci_config.c
> @@ -1027,8 +1027,11 @@ static int vfio_cap_len(struct vfio_pci_device *vdev, u8 cap, u8 pos)
>  
>  		if (PCI_X_CMD_VERSION(word)) {
>  			/* Test for extended capabilities */
> -			pci_read_config_dword(pdev, PCI_CFG_SPACE_SIZE, &dword);
> -			vdev->extended_caps = (dword != 0);
> +			if (pdev->cfg_size > PCI_CFG_SPACE_SIZE) {
> +				pci_read_config_dword(pdev, PCI_CFG_SPACE_SIZE,
> +						      &dword);
> +				vdev->extended_caps = (dword != 0);
> +			}
>  			return PCI_CAP_PCIX_SIZEOF_V2;
>  		} else
>  			return PCI_CAP_PCIX_SIZEOF_V0;
> @@ -1041,8 +1044,10 @@ static int vfio_cap_len(struct vfio_pci_device *vdev, u8 cap, u8 pos)
>  		return byte;
>  	case PCI_CAP_ID_EXP:
>  		/* Test for extended capabilities */
> -		pci_read_config_dword(pdev, PCI_CFG_SPACE_SIZE, &dword);
> -		vdev->extended_caps = (dword != 0);
> +		if (pdev->cfg_size > PCI_CFG_SPACE_SIZE) {
> +			pci_read_config_dword(pdev, PCI_CFG_SPACE_SIZE, &dword);
> +			vdev->extended_caps = (dword != 0);
> +		}
>  
>  		/* length based on version */
>  		if ((pcie_caps_reg(pdev) & PCI_EXP_FLAGS_VERS) == 1)
>
> --
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