x86, AMD IOMMU: add an emergency exit to the completion wait loop

To make the loop waiting for the completion wait command not wait forever this
patch adds a limit of cycles that loop.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Cc: iommu@lists.linux-foundation.org
Cc: bhavna.sarathy@amd.com
Cc: robert.richter@amd.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 9 insertions, 1 deletions

diff --git a/arch/x86/kernel/amd_iommu.c b/arch/x86/kernel/amd_iommu.c
index 9098f047c1a9..7fa2d5d57dd8 100644
--- a/arch/x86/kernel/amd_iommu.c
+++ b/arch/x86/kernel/amd_iommu.c
@@ -32,6 +32,8 @@
 #define to_pages(addr, size) \
          (round_up(((addr) & ~PAGE_MASK) + (size), PAGE_SIZE) >> PAGE_SHIFT)
 
+#define EXIT_LOOP_COUNT 10000000
+
 static DEFINE_RWLOCK(amd_iommu_devtable_lock);
 
 /*
@@ -106,6 +108,7 @@ static int iommu_completion_wait(struct amd_iommu *iommu)
         struct command cmd;
         volatile u64 ready = 0;
         unsigned long ready_phys = virt_to_phys(&ready);
+        unsigned long i = 0;
 
         memset(&cmd, 0, sizeof(cmd));
         cmd.data[0] = LOW_U32(ready_phys) | CMD_COMPL_WAIT_STORE_MASK;
@@ -120,8 +123,13 @@ static int iommu_completion_wait(struct amd_iommu *iommu)
         if (ret)
                 return ret;
 
-        while (!ready)
+        while (!ready && (i < EXIT_LOOP_COUNT)) {
+                ++i;
                 cpu_relax();
+        }
+
+        if (unlikely((i == EXIT_LOOP_COUNT) && printk_ratelimit()))
+                printk(KERN_WARNING "AMD IOMMU: Completion wait loop failed\n");
 
         return 0;
 }