linux-kernel - [PATCH 08/16] AMD IOMMU: add an emergency exit to the completion wait loop

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Date:	Fri, 11 Jul 2008 17:14:27 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	mingo@...hat.com, tglx@...utronix.de
CC:	linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
	bhavna.sarathy@....com, robert.richter@....com,
	Joerg Roedel <joerg.roedel@....com>
Subject: [PATCH 08/16] 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@....com>
---
 arch/x86/kernel/amd_iommu.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kernel/amd_iommu.c b/arch/x86/kernel/amd_iommu.c
index 9098f04..7fa2d5d 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;
 }
-- 
1.5.3.7


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