Re: [PATCH v1 1/2] iommu/amd: Fix IRQ unsafe locking in gdom allocation

[Ankit Soni]

On Thu, Jul 09, 2026 at 01:57:35PM -0600, Tycho Andersen wrote:
> From: "Tycho Andersen (AMD)" <tycho@xxxxxxxxxx>
> 
> Lockdep complains:
> 
>   [  259.410489] =====================================================
>   [  259.417287] WARNING: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected
>   [  259.424667] 7.0.0-g51db1d8d2113 #54 Not tainted
>   [  259.429718] -----------------------------------------------------
>   [  259.436516] qemu-system-x86/10143 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
>   [  259.444670] ff3b2b1c60305170 (&xa->xa_lock#25){+.+.}-{3:3}, at: __domain_flush_pages+0x17c/0x4b0
>   [  259.454485]
>                  and this task is already holding:
>   [  259.460991] ff3b2b1c98504cc0 (&domain->lock){-.-.}-{3:3}, at: amd_iommu_iotlb_sync+0x25/0x60
>   [  259.470408] which would create a new lock dependency:
>   [  259.476041]  (&domain->lock){-.-.}-{3:3} -> (&xa->xa_lock#25){+.+.}-{3:3}
>   [  259.483615]
>                  but this new dependency connects a HARDIRQ-irq-safe lock:
>   [  259.492447]  (&domain->lock){-.-.}-{3:3}
>   [  259.492449]
>                  ... which became HARDIRQ-irq-safe at:
>   [  259.503705]   lock_acquire+0xb6/0x2e0
>   [  259.507790]   _raw_spin_lock_irqsave+0x3e/0x60
>   [  259.512748]   amd_iommu_flush_iotlb_all+0x20/0x50
>   [  259.517996]   iommu_dma_free_iova.isra.0+0x1b8/0x1e0
>   [  259.523534]   __iommu_dma_unmap+0xc2/0x140
>   [  259.528100]   iommu_dma_unmap_phys+0x55/0xc0
>   [  259.532863]   dma_unmap_phys+0x274/0x2e0
>   [  259.537238]   dma_unmap_page_attrs+0x17/0x30
>   [  259.542000]   nvme_unmap_data+0x13e/0x280
>   [  259.546473]   nvme_pci_complete_batch+0x45/0x70
>   [  259.551524]   nvme_irq+0x83/0x90
>   [  259.555123]   __handle_irq_event_percpu+0x92/0x360
>   [  259.560466]   handle_irq_event+0x39/0x80
>   [  259.564841]   handle_edge_irq+0xb2/0x1a0
>   [  259.569214]   __common_interrupt+0x4e/0x130
>   [  259.573882]   common_interrupt+0x88/0xa0
>   [  259.578256]   asm_common_interrupt+0x27/0x40
>   [  259.583019]   cpuidle_enter_state+0x119/0x5d0
>   [  259.587877]   cpuidle_enter+0x2e/0x50
>   [  259.591962]   do_idle+0x153/0x2c0
>   [  259.595657]   cpu_startup_entry+0x29/0x30
>   [  259.600128]   start_secondary+0x118/0x150
>   [  259.604601]   common_startup_64+0x13e/0x141
>   [  259.609266]
>                  to a HARDIRQ-irq-unsafe lock:
>   [  259.615384]  (&xa->xa_lock#25){+.+.}-{3:3}
>   [  259.615386]
>                  ... which became HARDIRQ-irq-unsafe at:
>   [  259.627039] ...
>   [  259.627039]   lock_acquire+0xb6/0x2e0
>   [  259.633071]   _raw_spin_lock+0x2f/0x50
>   [  259.637250]   amd_iommu_alloc_domain_nested+0x140/0x3c0
>   [  259.643078]   iommufd_hwpt_alloc+0x272/0x800 [iommufd]
>   [  259.648813]   iommufd_fops_ioctl+0x14e/0x200 [iommufd]
>   [  259.654547]   __x64_sys_ioctl+0x9d/0xf0
>   ...
> 
> Since amd_iommu_domain_flush_pages() necessarily holds domain->lock to do the
> flush, switch the allocation side in gdom_info_load_or_alloc_locked() to
> HARDIRQ-safe allocation. The IOMMU_DESTROY->free path has the same issue,
> so switch that path to HARDIRQ-safe locking as well.
> 
> Fixes: 757d2b1fdf5b ("iommu/amd: Introduce gDomID-to-hDomID Mapping and handle parent domain invalidation")
> Signed-off-by: Tycho Andersen (AMD) <tycho@xxxxxxxxxx>

LGTM.

Reviewed-by: Ankit Soni <Ankit.Soni@xxxxxxx>