From: Joerg Roedel <jroedel@xxxxxxx> 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@xxxxxxx> Link: https://lore.kernel.org/r/20220204115537.3894-1-joro@xxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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) Patches currently in stable-queue which might be from jroedel@xxxxxxx are queue-4.9/iommu-amd-fix-loop-timeout-issue-in-iommu_ga_log_enable.patch