[PATCH kernel 2/2] powerpc/mm_iommu: Fix potential deadlock
Alexey Kardashevskiy
aik at ozlabs.ru
Fri Mar 29 16:46:41 AEDT 2019
Currently mm_iommu_do_alloc() is called in 2 cases:
- VFIO_IOMMU_SPAPR_REGISTER_MEMORY ioctl() for normal memory;
- vfio_pci_nvgpu_regops::mmap() for GPU memory.
One of the differences here is that the mmap() is called with mm::mmap_sem
help and mm_iommu_do_alloc() locks mm::mmap_sem itself (when adjusting
locked_vm and when pinning pages) which can potentially cause a deadlock.
We did not hit this yet because the mmap() path does not adjust
locked_vm and does not pin pages. However with CONFIG_DEBUG_LOCKDEP=y
there is an annoying warning (below, it is slightly confusing).
This makes a few changes to reduce the amount of time spent under a lock.
This holds mem_list_mutex only when looking or changing the mem list.
This means the list is checked twice now for the normal memory case -
before starting pinning and before adding the item to the list.
This changes mm_iommu_do_alloc() to only allocate and add an iommu memory
descriptor (used to deal with both normal and GPU memory in a rather
messy way).
This cleans the code in a way that mm_iommu_new() and mm_iommu_do_alloc()
do not need to test for (dev_hpa != MM_IOMMU_TABLE_INVALID_HPA) which
makes the code simpler.
This moves locked_vm decrementing from under mem_list_mutex for the same
reasons.
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
Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
---
arch/powerpc/mm/mmu_context_iommu.c | 128 ++++++++++++++--------------
1 file changed, 65 insertions(+), 63 deletions(-)
diff --git a/arch/powerpc/mm/mmu_context_iommu.c b/arch/powerpc/mm/mmu_context_iommu.c
index 6b351c79713b..36a826e23d45 100644
--- a/arch/powerpc/mm/mmu_context_iommu.c
+++ b/arch/powerpc/mm/mmu_context_iommu.c
@@ -96,50 +96,59 @@ static bool mm_iommu_find(struct mm_struct *mm, unsigned long ua,
return false;
}
-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)
+/* Must be called with &mem_list_mutex held */
+static int mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua,
+ unsigned long entries, unsigned long dev_hpa,
+ unsigned int mem_pageshift, phys_addr_t *hpas,
+ struct mm_iommu_table_group_mem_t **pmem)
{
struct mm_iommu_table_group_mem_t *mem;
- long i, ret, locked_entries = 0;
+
+ if (mm_iommu_find(mm, ua, entries))
+ return -EINVAL;
+
+ mem = kzalloc(sizeof(*mem), GFP_KERNEL);
+ if (!mem)
+ return -ENOMEM;
+
+ atomic64_set(&mem->mapped, 1);
+ mem->dev_hpa = dev_hpa;
+ mem->used = 1;
+ mem->ua = ua;
+ mem->entries = entries;
+ mem->pageshift = mem_pageshift;
+ mem->hpas = hpas;
+ list_add_rcu(&mem->next, &mm->context.iommu_group_mem_list);
+ *pmem = mem;
+
+ return 0;
+}
+
+long mm_iommu_new(struct mm_struct *mm, unsigned long ua, unsigned long entries,
+ struct mm_iommu_table_group_mem_t **pmem)
+{
+ long i, ret = 0, locked_entries = 0;
unsigned int pageshift, mem_pageshift;
struct page **hpages;
phys_addr_t *hpas;
mutex_lock(&mem_list_mutex);
-
if (mm_iommu_find(mm, ua, entries)) {
- ret = -EINVAL;
- goto unlock_exit;
+ mutex_unlock(&mem_list_mutex);
+ return -EINVAL;
}
+ mutex_unlock(&mem_list_mutex);
- if (dev_hpa == MM_IOMMU_TABLE_INVALID_HPA) {
- ret = mm_iommu_adjust_locked_vm(mm, entries, true);
- if (ret)
- goto unlock_exit;
+ ret = mm_iommu_adjust_locked_vm(mm, entries, true);
+ if (ret)
+ return ret;
- locked_entries = entries;
- }
-
- mem = kzalloc(sizeof(*mem), GFP_KERNEL);
- if (!mem) {
- ret = -ENOMEM;
- goto unlock_exit;
- }
-
- if (dev_hpa != MM_IOMMU_TABLE_INVALID_HPA) {
- mem_pageshift = __ffs(dev_hpa | (entries << PAGE_SHIFT));
- hpas = NULL;
- mem->dev_hpa = dev_hpa;
- goto good_exit;
- }
- mem->dev_hpa = MM_IOMMU_TABLE_INVALID_HPA;
+ locked_entries = entries;
hpages = vzalloc(array_size(entries, sizeof(hpages[0])));
if (!hpages) {
- kfree(mem);
ret = -ENOMEM;
- goto unlock_exit;
+ goto cleanup_exit;
}
down_read(&mm->mmap_sem);
@@ -149,11 +158,8 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua,
/* free the reference taken */
for (i = 0; i < ret; i++)
put_page(hpages[i]);
-
- vfree(hpages);
- kfree(mem);
ret = -EFAULT;
- goto unlock_exit;
+ goto cleanup_exit;
}
/*
@@ -184,40 +190,35 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua,
hpas[i] = page_to_pfn(page) << PAGE_SHIFT;
}
-good_exit:
- ret = 0;
- atomic64_set(&mem->mapped, 1);
- mem->used = 1;
- mem->ua = ua;
- mem->entries = entries;
- mem->hpas = hpas;
- mem->pageshift = mem_pageshift;
- *pmem = mem;
-
- list_add_rcu(&mem->next, &mm->context.iommu_group_mem_list);
-
-unlock_exit:
- if (locked_entries && ret)
- mm_iommu_adjust_locked_vm(mm, locked_entries, false);
-
+ mutex_lock(&mem_list_mutex);
+ ret = mm_iommu_do_alloc(mm, ua, entries, MM_IOMMU_TABLE_INVALID_HPA,
+ mem_pageshift, hpas, pmem);
mutex_unlock(&mem_list_mutex);
+ if (ret)
+ goto cleanup_exit;
+ return 0;
+
+cleanup_exit:
+ mm_iommu_adjust_locked_vm(mm, locked_entries, false);
+ vfree(hpages);
+
return ret;
}
-
-long mm_iommu_new(struct mm_struct *mm, unsigned long ua, unsigned long entries,
- struct mm_iommu_table_group_mem_t **pmem)
-{
- return mm_iommu_do_alloc(mm, ua, entries, MM_IOMMU_TABLE_INVALID_HPA,
- pmem);
-}
EXPORT_SYMBOL_GPL(mm_iommu_new);
long mm_iommu_newdev(struct mm_struct *mm, unsigned long ua,
unsigned long entries, unsigned long dev_hpa,
struct mm_iommu_table_group_mem_t **pmem)
{
- return mm_iommu_do_alloc(mm, ua, entries, dev_hpa, pmem);
+ int ret;
+
+ mutex_lock(&mem_list_mutex);
+ ret = mm_iommu_do_alloc(mm, ua, entries, dev_hpa,
+ __ffs(dev_hpa | (entries << PAGE_SHIFT)), NULL, pmem);
+ mutex_unlock(&mem_list_mutex);
+
+ return ret;
}
EXPORT_SYMBOL_GPL(mm_iommu_newdev);
@@ -270,10 +271,13 @@ 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);
+ if (mem->dev_hpa == MM_IOMMU_TABLE_INVALID_HPA)
+ unlock_entries = mem->entries;
+
if (mem->used == 0) {
ret = -ENOENT;
goto unlock_exit;
@@ -292,16 +296,14 @@ long mm_iommu_put(struct mm_struct *mm, struct mm_iommu_table_group_mem_t *mem)
}
/* @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);
+ if (!ret)
+ mm_iommu_adjust_locked_vm(mm, unlock_entries, false);
+
return ret;
}
EXPORT_SYMBOL_GPL(mm_iommu_put);
--
2.17.1
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