linux-kernel - [PATCH 5.10 31/74] iommu/amd: Fix loop timeout issue in iommu_ga_log

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Message-Id: <20220207103758.262021970@linuxfoundation.org>
Date:   Mon,  7 Feb 2022 12:06:29 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Joerg Roedel <jroedel@...e.de>
Subject: [PATCH 5.10 31/74] iommu/amd: Fix loop timeout issue in iommu_ga_log_enable()

From: Joerg Roedel <jroedel@...e.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@...e.de>
Link: https://lore.kernel.org/r/20220204115537.3894-1-joro@8bytes.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/iommu/amd/init.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -20,6 +20,7 @@
 #include <linux/export.h>
 #include <linux/kmemleak.h>
 #include <linux/mem_encrypt.h>
+#include <linux/iopoll.h>
 #include <asm/pci-direct.h>
 #include <asm/iommu.h>
 #include <asm/apic.h>
@@ -833,6 +834,7 @@ 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 (WARN_ON(i >= LOOP_TIMEOUT))