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authorAlexey Kardashevskiy <aik@ozlabs.ru>2019-04-03 15:12:32 +1100
committerMichael Ellerman <mpe@ellerman.id.au>2019-04-17 21:36:50 +1000
commiteb9d7a62c38628ab0ba6e59d22d7cb7930e415d1 (patch)
treeb9090381a7d280f818bec83fd271cedfaf3c552c /arch
parent8adddf349fda0d3de2f6bb41ddf838cbf36a8ad2 (diff)
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 <aik@ozlabs.ru> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch')
-rw-r--r--arch/powerpc/mm/mmu_context_iommu.c75
1 files 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);