[PATCH] iommu/amd: fix a crash in iova_magazine_free_pfns

[Qian Cai]

When a system is under heavy memory pressure, the allocation in
alloc_iova_fast() could still fail even flush_rcache=true, and then
causes dma_ops_alloc_iova() return 0.

pqi_scsi_queue_command
  pqi_raid_submit_scsi_cmd_with_io_request
    scsi_dma_map
      map_sg
        dma_ops_alloc_iova
         alloc_iova_fast

Later, map_sg()->iommu_map_page() would probably fail due to the invalid
PFN 0, and call free_iova_fast()->iova_rcache_insert() to insert it to
the rcache. Finally, it will trigger the BUG_ON(!iova) here.

    kernel BUG at drivers/iommu/iova.c:801!
    Workqueue: kblockd blk_mq_run_work_fn
    RIP: 0010:iova_magazine_free_pfns+0x7d/0xc0
    Call Trace:
     free_cpu_cached_iovas+0xbd/0x150
     alloc_iova_fast+0x8c/0xba
     dma_ops_alloc_iova.isra.6+0x65/0xa0
     map_sg+0x8c/0x2a0
     scsi_dma_map+0xc6/0x160
     pqi_aio_submit_io+0x1f6/0x440 [smartpqi]
     pqi_scsi_queue_command+0x90c/0xdd0 [smartpqi]
     scsi_queue_rq+0x79c/0x1200
     blk_mq_dispatch_rq_list+0x4dc/0xb70
     blk_mq_sched_dispatch_requests+0x249/0x310
     __blk_mq_run_hw_queue+0x128/0x200
     blk_mq_run_work_fn+0x27/0x30
     process_one_work+0x522/0xa10
     worker_thread+0x63/0x5b0
     kthread+0x1d2/0x1f0
     ret_from_fork+0x22/0x40

Fix it by validating the return from the 2nd alloc_iova_fast() in
dma_ops_alloc_iova(), so map_sg() could handle the error condition
immediately.

Signed-off-by: Qian Cai <cai@xxxxxx>
---
 drivers/iommu/amd_iommu.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index 73740b969e62..f24c689b4e01 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -1697,6 +1697,8 @@ static unsigned long dma_ops_alloc_iova(struct device *dev,
 	if (!pfn)
 		pfn = alloc_iova_fast(&dma_dom->iovad, pages,
 				      IOVA_PFN(dma_mask), true);
+	if (!pfn)
+		return DMA_MAPPING_ERROR;
 
 	return (pfn << PAGE_SHIFT);
 }
-- 
1.8.3.1