On Mon, Jul 20, 2015 at 07:13:57PM -0500, Bjorn Helgaas wrote:
> We check the ATS state (enabled/disabled) and fetch the PCI ATS Invalidate
> Queue Depth in performance-sensitive paths. It's easy to cache these,
> which removes dependencies on PCI.
>
> Remember the ATS enabled state. When enabling, read the queue depth once
> and cache it in the device_domain_info struct. This is similar to what
> amd_iommu.c does.
>
> Signed-off-by: Bjorn Helgaas <bhelg...@google.com>
> ---
> drivers/iommu/intel-iommu.c | 26 ++++++++++++++++----------
> 1 file changed, 16 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index a98a7b2..50832f1 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -408,6 +408,10 @@ struct device_domain_info {
> struct list_head global; /* link to global list */
> u8 bus; /* PCI bus number */
> u8 devfn; /* PCI devfn number */
> + struct {
> + int enabled:1;
> + u8 qdep;
> + } ats; /* ATS state */
> struct device *dev; /* it's NULL for PCIe-to-PCI bridge */
> struct intel_iommu *iommu; /* IOMMU used by this device */
> struct dmar_domain *domain; /* pointer to domain */
> @@ -1391,19 +1395,26 @@ iommu_support_dev_iotlb (struct dmar_domain *domain,
> struct intel_iommu *iommu,
>
> static void iommu_enable_dev_iotlb(struct device_domain_info *info)
> {
> + struct pci_dev *pdev;
> +
> if (!info || !dev_is_pci(info->dev))
> return;
>
> - pci_enable_ats(to_pci_dev(info->dev), VTD_PAGE_SHIFT);
> + pdev = to_pci_dev(info->dev);
> + if (pci_enable_ats(pdev, VTD_PAGE_SHIFT))
> + return;
> +
> + info->ats.enabled = 1;
> + info->ats.qdep = pci_ats_queue_depth(pdev);
Hmm, this is a place where the relaxed error handling in
pci_enable_ats() can get problematic. If ATS is (by accident or a bug
elsewhere) already enabled an the function returns -EINVAL, the IOMMU
driver considers ATS disabled and doesn't flush the IO/TLBs of the
device. This can cause data corruption later on, so we should make sure
that info->ats.enabled is consistent with pdev->ats_enabled.
Joerg
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