linux-kernel - Re: [PATCH 0/2] iommu/vt-d: Fix lockdep splat in intel_iommu

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Date:   Tue, 18 Oct 2022 15:57:56 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>, Kevin Tian <kevin.tian@...el.com>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] iommu/vt-d: Fix lockdep splat in intel_iommu_init()

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