Re: [PATCH v4 4/7] PCI: Don't update VF BARs while VF memory space is enabled

[Gavin Shan <gwshan@linux.vnet.ibm.com>]

On Mon, Nov 28, 2016 at 10:15:21PM -0600, Bjorn Helgaas wrote:
>If we update a VF BAR while it's enabled, there are two potential problems:
>
>  1) Any driver that's using the VF has a cached BAR value that is stale
>     after the update, and
>
>  2) We can't update 64-bit BARs atomically, so the intermediate state
>     (new lower dword with old upper dword) may conflict with another
>     device, and an access by a driver unrelated to the VF may cause a bus
>     error.
>
>Warn about attempts to update VF BARs while they are enabled.  This is a
>programming error, so use dev_WARN() to get a backtrace.
>
>Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>

>---
> drivers/pci/iov.c |    8 ++++++++
> 1 file changed, 8 insertions(+)
>
>diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
>index d00ed5c..a800ba2 100644
>--- a/drivers/pci/iov.c
>+++ b/drivers/pci/iov.c
>@@ -584,6 +584,7 @@ void pci_iov_update_resource(struct pci_dev *dev, int resno)
> 	struct resource *res = dev->resource + resno;
> 	int vf_bar = resno - PCI_IOV_RESOURCES;
> 	struct pci_bus_region region;
>+	u16 cmd;
> 	u32 new;
> 	int reg;
>
>@@ -595,6 +596,13 @@ void pci_iov_update_resource(struct pci_dev *dev, int resno)
> 	if (!iov)
> 		return;
>
>+	pci_read_config_word(dev, iov->pos + PCI_SRIOV_CTRL, &cmd);
>+	if ((cmd & PCI_SRIOV_CTRL_VFE) && (cmd & PCI_SRIOV_CTRL_MSE)) {
>+		dev_WARN(&dev->dev, "can't update enabled VF BAR%d %pR\n",
>+			 vf_bar, res);
>+		return;
>+	}
>+
> 	/*
> 	 * Ignore unimplemented BARs, unused resource slots for 64-bit
> 	 * BARs, and non-movable resources, e.g., those described via
>
>--
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