linux-kernel - [PATCH v2] iommu/amd: Fix loop timeout issue in iommu_ga_log

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Message-Id: <20220204115537.3894-1-joro@8bytes.org>
Date:   Fri,  4 Feb 2022 12:55:37 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Will Deacon <will@...nel.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Joerg Roedel <jroedel@...e.de>
Subject: [PATCH v2] iommu/amd: Fix loop timeout issue in iommu_ga_log_enable()

From: Joerg Roedel <jroedel@...e.de>

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@...e.de>
---
 drivers/iommu/amd/init.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index dc338acf3338..b10fb52ea442 100644
--- 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))
-- 
2.34.1