linux-kernel - [PATCH] intel-iommu: Turn off translations at shutdown

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Message-Id: <20191107205914.10611-1-deepa.kernel@gmail.com>
Date:   Thu,  7 Nov 2019 12:59:14 -0800
From:   Deepa Dinamani <deepa.kernel@...il.com>
To:     joro@...tes.org, linux-kernel@...r.kernel.org
Cc:     dwmw2@...radead.org, iommu@...ts.linux-foundation.org
Subject: [PATCH] intel-iommu: Turn off translations at shutdown

The intel-iommu driver assumes that the iommu state is
cleaned up at the start of the new kernel.
But, when we try to kexec boot something other than the
Linux kernel, the cleanup cannot be relied upon.
Hence, cleanup before we go down for reboot.

Keeping the cleanup at initialization also, in case BIOS
leaves the IOMMU enabled.

I considered turning off iommu only during kexec reboot,
but a clean shutdown seems always a good idea. But if
someone wants to make it conditional, we can do that.

Tested that before, the info message
'DMAR: Translation was enabled for <iommu> but we are not in kdump mode'
would be reported for each iommu. The message will not appear when the
DMA-remapping is not enabled on entry to the kernel.

Signed-off-by: Deepa Dinamani <deepa.kernel@...il.com>
---
 drivers/iommu/intel-iommu.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index fe8097078669..f0636b263722 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -4764,6 +4764,26 @@ static void intel_disable_iommus(void)
 		iommu_disable_translation(iommu);
 }

+static void intel_iommu_shutdown(void)
+{
+	struct dmar_drhd_unit *drhd;
+	struct intel_iommu *iommu = NULL;
+
+	if (no_iommu || dmar_disabled)
+		return;
+
+	down_write(&dmar_global_lock);
+
+	/* Disable PMRs explicitly here. */
+	for_each_iommu(iommu, drhd)
+		iommu_disable_protect_mem_regions(iommu);
+
+	/* Make sure the IOMMUs are switched off */
+	intel_disable_iommus();
+
+	up_write(&dmar_global_lock);
+}
+
 static inline struct intel_iommu *dev_to_intel_iommu(struct device *dev)
 {
 	struct iommu_device *iommu_dev = dev_to_iommu_device(dev);
@@ -5013,6 +5033,8 @@ int __init intel_iommu_init(void)
 	}
 	up_write(&dmar_global_lock);

+	x86_platform.iommu_shutdown = intel_iommu_shutdown;
+
 #if defined(CONFIG_X86) && defined(CONFIG_SWIOTLB)
 	/*
 	 * If the system has no untrusted device or the user has decided
-- 
2.17.1