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

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Date:   Mon, 31 Jan 2022 17:17:49 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     iommu@...ts.linux-foundation.org
Cc:     Joerg Roedel <joro@...tes.org>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Joerg Roedel <jroedel@...e.de>
Subject: [PATCH] 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.

Fixes: 8bda0cfbdc1a ("iommu/amd: Detect and initialize guest vAPIC log")
Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 drivers/iommu/amd/init.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index dc338acf3338..d2e09d53851f 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -834,6 +834,7 @@ 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(1);
 	}
 
 	if (WARN_ON(i >= LOOP_TIMEOUT))
-- 
2.34.1