Re: [PATCH 0/2] iommu/vt-d: Fix lockdep splat in intel_iommu_init()

Alex Williamson
2022-10-18T21:58:09Z

On Tue, 27 Sep 2022 13:31:07 +0800
Lu Baolu <baolu.lu@linux.intel.com> wrote:

> Hi folks,
>
> As commit c919739ce472 ("iommu/vt-d: Handle race between registration
> and device probe") highlights, a lockdep splat issue happens after
> moving iommu probing device process into iommu_device_register().
>
> This is due to a conflict that get_resv_regions wants hold the
> dmar_global_lock, but it's also possible to be called from within a
> section where intel_iommu_init() already holds the lock.
>
> Historically, before commit 5f64ce5411b46 ("iommu/vt-d: Duplicate
> iommu_resv_region objects per device list"), the rcu_lock is used in
> get_resv_regions. This commit converted it to dmar_global_lock in order
> to allowing sleeping in iommu_alloc_resv_region().
>
> This aims to fix the lockdep issue by making iommu_alloc_resv_region()
> available in critical section and rolling dmar_global_lock back to rcu
> lock in get_resv_regions of the Intel IOMMU driver.
>
> Best regards,
> baolu
>
> Lu Baolu (2):
> iommu: Add gfp parameter to iommu_alloc_resv_region
> iommu/vt-d: Use rcu_lock in get_resv_regions
>
> include/linux/iommu.h | 2 +-
> drivers/acpi/arm64/iort.c | 3 ++-
> drivers/iommu/amd/iommu.c | 7 ++++---
> drivers/iommu/apple-dart.c | 2 +-
> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 2 +-
> drivers/iommu/arm/arm-smmu/arm-smmu.c | 2 +-
> drivers/iommu/intel/iommu.c | 12 +++++++-----
> drivers/iommu/iommu.c | 7 ++++---
> drivers/iommu/mtk_iommu.c | 3 ++-
> drivers/iommu/virtio-iommu.c | 9 ++++++---
> 10 files changed, 29 insertions(+), 20 deletions(-)

Resolves the regression for me. Hopefully Joerg will queue this for
6.1-rc. Thanks!

Tested-by: Alex Williamson <alex.williamson@redhat.com>