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SubjectRE: [RFC PATCH] iommu/vt-d: Exclude known RMRRs from reserved ranges
Date
> From: Alex Williamson
> Sent: Wednesday, June 6, 2018 3:07 AM
>
> device_is_rmrr_locked() allows graphics and USB devices to participate
> in the IOMMU API despite, and ignoring their RMRR association, however
> intel_iommu_get_resv_regions() still includes the RMRRs as unavailable
> IOVA space for the device. Are we ignoring the RMRR for these devices
> or are we not? If vfio starts consuming reserved regions, perhaps we
> no longer need to consider devices with RMRRs excluded from the IOMMU
> API interface, but we have a transitional problem that these allowed
> devices still impose incompatible IOVA restrictions per the reserved
> region reporting. Dive further down the rabbit hole by also ignoring
> RMRRs for "known" devices in the reserved region reporting.

intel_iommu_get_resv_regions is used not just for IOMMU API. I'm
afraid doing so will make RMRR completely ignored, even in normal
DMA API path...

>
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> ---
> drivers/iommu/intel-iommu.c | 35 +++++++++++++++++++++--------------
> 1 file changed, 21 insertions(+), 14 deletions(-)
>
> If this is the approach we want to take, I could pull this in via the
> vfio tree, along with Shameer's patches which expose an IOVA list and
> enforce it to userspace, otherwise I'm afraid Shameer's patches will
> be blocked a while longer. Thanks,
>
> Alex
>
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 749d8f235346..f312f93199c5 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -2864,19 +2864,24 @@ static bool device_has_rmrr(struct device *dev)
> * any use of the RMRR regions will be torn down before assigning the
> device
> * to a guest.
> */
> -static bool device_is_rmrr_locked(struct device *dev)
> +static bool rmrr_is_ignored(struct device *dev)
> {
> - if (!device_has_rmrr(dev))
> - return false;
> -
> if (dev_is_pci(dev)) {
> struct pci_dev *pdev = to_pci_dev(dev);
>
> if (IS_USB_DEVICE(pdev) || IS_GFX_DEVICE(pdev))
> - return false;
> + return true;
> }
>
> - return true;
> + return false;
> +}
> +
> +static bool device_is_rmrr_locked(struct device *dev)
> +{
> + if (!device_has_rmrr(dev))
> + return false;
> +
> + return !rmrr_is_ignored(dev);
> }
>
> static int iommu_should_identity_map(struct device *dev, int startup)
> @@ -5141,17 +5146,19 @@ static void
> intel_iommu_get_resv_regions(struct device *device,
> struct device *i_dev;
> int i;
>
> - rcu_read_lock();
> - for_each_rmrr_units(rmrr) {
> - for_each_active_dev_scope(rmrr->devices, rmrr-
> >devices_cnt,
> - i, i_dev) {
> - if (i_dev != device)
> - continue;
> + if (!rmrr_is_ignored(device)) {
> + rcu_read_lock();
> + for_each_rmrr_units(rmrr) {
> + for_each_active_dev_scope(rmrr->devices,
> + rmrr->devices_cnt, i, i_dev)
> {
> + if (i_dev != device)
> + continue;
>
> - list_add_tail(&rmrr->resv->list, head);
> + list_add_tail(&rmrr->resv->list, head);
> + }
> }
> + rcu_read_unlock();
> }
> - rcu_read_unlock();
>
> reg = iommu_alloc_resv_region(IOAPIC_RANGE_START,
> IOAPIC_RANGE_END -
> IOAPIC_RANGE_START + 1,

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