iommu/amd: Fix loop timeout issue in iommu_ga_log_enable()

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

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index dc338acf33385b0c4bf59cf0979b97598124f7df..b10fb52ea44288747e0d992385a7b656541d92b7 100644 (file)
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -21,6 +21,7 @@
 #include <linux/export.h>
 #include <linux/kmemleak.h>
 #include <linux/cc_platform.h>
+#include <linux/iopoll.h>
 #include <asm/pci-direct.h>
 #include <asm/iommu.h>
 #include <asm/apic.h>
@@ -834,6 +835,7 @@ static int iommu_ga_log_enable(struct amd_iommu *iommu)
                status = readl(iommu->mmio_base + MMIO_STATUS_OFFSET);
                if (status & (MMIO_STATUS_GALOG_RUN_MASK))
                        break;
+               udelay(10);
        }
 
        if (WARN_ON(i >= LOOP_TIMEOUT))