From eb9d7a62c38628ab0ba6e59d22d7cb7930e415d1 Mon Sep 17 00:00:00 2001 From: Alexey Kardashevskiy Date: Wed, 3 Apr 2019 15:12:32 +1100 Subject: [PATCH] powerpc/mm_iommu: Fix potential deadlock Currently mm_iommu_do_alloc() is called in 2 cases: - VFIO_IOMMU_SPAPR_REGISTER_MEMORY ioctl() for normal memory: this locks &mem_list_mutex and then locks mm::mmap_sem several times when adjusting locked_vm or pinning pages; - vfio_pci_nvgpu_regops::mmap() for GPU memory: this is called with mm::mmap_sem held already and it locks &mem_list_mutex. So one can craft a userspace program to do special ioctl and mmap in 2 threads concurrently and cause a deadlock which lockdep warns about (below). We did not hit this yet because QEMU constructs the machine in a single thread. This moves the overlap check next to where the new entry is added and reduces the amount of time spent with &mem_list_mutex held. This moves locked_vm adjustment from under &mem_list_mutex. This relies on mm_iommu_adjust_locked_vm() doing nothing when entries==0. This is one of the lockdep warnings: ====================================================== WARNING: possible circular locking dependency detected 5.1.0-rc2-le_nv2_aikATfstn1-p1 #363 Not tainted ------------------------------------------------------ qemu-system-ppc/8038 is trying to acquire lock: 000000002ec6c453 (mem_list_mutex){+.+.}, at: mm_iommu_do_alloc+0x70/0x490 but task is already holding lock: 00000000fd7da97f (&mm->mmap_sem){++++}, at: vm_mmap_pgoff+0xf0/0x160 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&mm->mmap_sem){++++}: lock_acquire+0xf8/0x260 down_write+0x44/0xa0 mm_iommu_adjust_locked_vm.part.1+0x4c/0x190 mm_iommu_do_alloc+0x310/0x490 tce_iommu_ioctl.part.9+0xb84/0x1150 [vfio_iommu_spapr_tce] vfio_fops_unl_ioctl+0x94/0x430 [vfio] do_vfs_ioctl+0xe4/0x930 ksys_ioctl+0xc4/0x110 sys_ioctl+0x28/0x80 system_call+0x5c/0x70 -> #0 (mem_list_mutex){+.+.}: __lock_acquire+0x1484/0x1900 lock_acquire+0xf8/0x260 __mutex_lock+0x88/0xa70 mm_iommu_do_alloc+0x70/0x490 vfio_pci_nvgpu_mmap+0xc0/0x130 [vfio_pci] vfio_pci_mmap+0x198/0x2a0 [vfio_pci] vfio_device_fops_mmap+0x44/0x70 [vfio] mmap_region+0x5d4/0x770 do_mmap+0x42c/0x650 vm_mmap_pgoff+0x124/0x160 ksys_mmap_pgoff+0xdc/0x2f0 sys_mmap+0x40/0x80 system_call+0x5c/0x70 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&mm->mmap_sem); lock(mem_list_mutex); lock(&mm->mmap_sem); lock(mem_list_mutex); *** DEADLOCK *** 1 lock held by qemu-system-ppc/8038: #0: 00000000fd7da97f (&mm->mmap_sem){++++}, at: vm_mmap_pgoff+0xf0/0x160 Fixes: c10c21efa4bc ("powerpc/vfio/iommu/kvm: Do not pin device memory", 2018-12-19) Signed-off-by: Alexey Kardashevskiy Signed-off-by: Michael Ellerman --- arch/powerpc/mm/mmu_context_iommu.c | 75 +++++++++++++++-------------- 1 file changed, 39 insertions(+), 36 deletions(-) diff --git a/arch/powerpc/mm/mmu_context_iommu.c b/arch/powerpc/mm/mmu_context_iommu.c index e7a9c4f6bfca..9d9be850f8c2 100644 --- a/arch/powerpc/mm/mmu_context_iommu.c +++ b/arch/powerpc/mm/mmu_context_iommu.c @@ -95,28 +95,14 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua, unsigned long entries, unsigned long dev_hpa, struct mm_iommu_table_group_mem_t **pmem) { - struct mm_iommu_table_group_mem_t *mem; - long i, ret, locked_entries = 0; + struct mm_iommu_table_group_mem_t *mem, *mem2; + long i, ret, locked_entries = 0, pinned = 0; unsigned int pageshift; - mutex_lock(&mem_list_mutex); - - list_for_each_entry_rcu(mem, &mm->context.iommu_group_mem_list, - next) { - /* Overlap? */ - if ((mem->ua < (ua + (entries << PAGE_SHIFT))) && - (ua < (mem->ua + - (mem->entries << PAGE_SHIFT)))) { - ret = -EINVAL; - goto unlock_exit; - } - - } - if (dev_hpa == MM_IOMMU_TABLE_INVALID_HPA) { ret = mm_iommu_adjust_locked_vm(mm, entries, true); if (ret) - goto unlock_exit; + return ret; locked_entries = entries; } @@ -150,15 +136,10 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua, down_read(&mm->mmap_sem); ret = get_user_pages_longterm(ua, entries, FOLL_WRITE, mem->hpages, NULL); up_read(&mm->mmap_sem); + pinned = ret > 0 ? ret : 0; if (ret != entries) { - /* free the reference taken */ - for (i = 0; i < ret; i++) - put_page(mem->hpages[i]); - - vfree(mem->hpas); - kfree(mem); ret = -EFAULT; - goto unlock_exit; + goto free_exit; } pageshift = PAGE_SHIFT; @@ -183,21 +164,43 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua, } good_exit: - ret = 0; atomic64_set(&mem->mapped, 1); mem->used = 1; mem->ua = ua; mem->entries = entries; - *pmem = mem; - list_add_rcu(&mem->next, &mm->context.iommu_group_mem_list); + mutex_lock(&mem_list_mutex); -unlock_exit: - if (locked_entries && ret) - mm_iommu_adjust_locked_vm(mm, locked_entries, false); + list_for_each_entry_rcu(mem2, &mm->context.iommu_group_mem_list, next) { + /* Overlap? */ + if ((mem2->ua < (ua + (entries << PAGE_SHIFT))) && + (ua < (mem2->ua + + (mem2->entries << PAGE_SHIFT)))) { + ret = -EINVAL; + mutex_unlock(&mem_list_mutex); + goto free_exit; + } + } + + list_add_rcu(&mem->next, &mm->context.iommu_group_mem_list); mutex_unlock(&mem_list_mutex); + *pmem = mem; + + return 0; + +free_exit: + /* free the reference taken */ + for (i = 0; i < pinned; i++) + put_page(mem->hpages[i]); + + vfree(mem->hpas); + kfree(mem); + +unlock_exit: + mm_iommu_adjust_locked_vm(mm, locked_entries, false); + return ret; } @@ -266,7 +269,7 @@ static void mm_iommu_release(struct mm_iommu_table_group_mem_t *mem) long mm_iommu_put(struct mm_struct *mm, struct mm_iommu_table_group_mem_t *mem) { long ret = 0; - unsigned long entries, dev_hpa; + unsigned long unlock_entries = 0; mutex_lock(&mem_list_mutex); @@ -287,17 +290,17 @@ long mm_iommu_put(struct mm_struct *mm, struct mm_iommu_table_group_mem_t *mem) goto unlock_exit; } + if (mem->dev_hpa == MM_IOMMU_TABLE_INVALID_HPA) + unlock_entries = mem->entries; + /* @mapped became 0 so now mappings are disabled, release the region */ - entries = mem->entries; - dev_hpa = mem->dev_hpa; mm_iommu_release(mem); - if (dev_hpa == MM_IOMMU_TABLE_INVALID_HPA) - mm_iommu_adjust_locked_vm(mm, entries, false); - unlock_exit: mutex_unlock(&mem_list_mutex); + mm_iommu_adjust_locked_vm(mm, unlock_entries, false); + return ret; } EXPORT_SYMBOL_GPL(mm_iommu_put); -- 2.45.2