[PATCH 4.9 37/48] iommu/amd: Fix loop timeout issue in iommu_ga_log_enable()

Greg Kroah-Hartman
2022-02-07T11:14:00Z

From: Joerg Roedel <jroedel@suse.de>

commit 9b45a7738eec52bf0f5d8d3d54e822962781c5f2 upstream.

The polling loop for the register change in iommu_ga_log_enable() needs
to have a udelay() in it. Otherwise the CPU might be faster than the
IOMMU hardware and wrongly trigger the WARN_ON() further down the code
stream. Use a 10us for udelay(), has there is some hardware where
activation of the GA log can take more than a 100ms.

A future optimization should move the activation check of the GA log
to the point where it gets used for the first time. But that is a
bigger change and not suitable for a fix.

Fixes: 8bda0cfbdc1a ("iommu/amd: Detect and initialize guest vAPIC log")
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Link: https://lore.kernel.org/r/20220204115537.3894-1-joro@8bytes.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/iommu/amd_iommu_init.c | 2 ++
1 file changed, 2 insertions(+)

--- a/drivers/iommu/amd_iommu_init.c
+++ b/drivers/iommu/amd_iommu_init.c
@@ -28,6 +28,7 @@
#include <linux/amd-iommu.h>
#include <linux/export.h>
#include <linux/iommu.h>
+#include <linux/iopoll.h>
#include <asm/pci-direct.h>
#include <asm/iommu.h>
#include <asm/gart.h>
@@ -715,6 +716,7 @@ static int iommu_ga_log_enable(struct am
status = readl(iommu->mmio_base + MMIO_STATUS_OFFSET);
if (status & (MMIO_STATUS_GALOG_RUN_MASK))
break;
+ udelay(10);
}

if (i >= LOOP_TIMEOUT)