linux-kernel - [PATCH] x86/dma: Tear down DMA ops on driver unbind

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Message-Id: <20210414082633.877461-1-jean-philippe@linaro.org>
Date:   Wed, 14 Apr 2021 10:26:34 +0200
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org
Cc:     hpa@...or.com, linux-kernel@...r.kernel.org, joro@...tes.org,
        will@...nel.org, iommu@...ts.linux-foundation.org,
        robin.murphy@....com, hch@....de,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: [PATCH] x86/dma: Tear down DMA ops on driver unbind

Since commit 08a27c1c3ecf ("iommu: Add support to change default domain
of an iommu group") a user can switch a device between IOMMU and direct
DMA through sysfs. This doesn't work for AMD IOMMU at the moment because
dev->dma_ops is not cleared when switching from a DMA to an identity
IOMMU domain. The DMA layer thus attempts to use the dma-iommu ops on an
identity domain, causing an oops:

  # echo 0000:00:05.0 > /sys/sys/bus/pci/drivers/e1000e/unbind
  # echo identity > /sys/bus/pci/devices/0000:00:05.0/iommu_group/type
  # echo 0000:00:05.0 > /sys/sys/bus/pci/drivers/e1000e/bind
   ...
  [  190.017587] BUG: kernel NULL pointer dereference, address: 0000000000000028
   ...
  [  190.027375] Call Trace:
  [  190.027561]  iommu_dma_alloc+0xd0/0x100
  [  190.027840]  e1000e_setup_tx_resources+0x56/0x90
  [  190.028173]  e1000e_open+0x75/0x5b0

Implement arch_teardown_dma_ops() on x86 to clear the device's dma_ops
pointer during driver unbind.

Fixes: 08a27c1c3ecf ("iommu: Add support to change default domain of an iommu group")
Signed-off-by: Jean-Philippe Brucker <jean-philippe@...aro.org>
---
 arch/x86/Kconfig          | 1 +
 arch/x86/kernel/pci-dma.c | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 2792879d398e..2c90f8de3e20 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -85,6 +85,7 @@ config X86
 	select ARCH_HAS_STRICT_MODULE_RWX
 	select ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
 	select ARCH_HAS_SYSCALL_WRAPPER
+	select ARCH_HAS_TEARDOWN_DMA_OPS	if IOMMU_DMA
 	select ARCH_HAS_UBSAN_SANITIZE_ALL
 	select ARCH_HAS_DEBUG_WX
 	select ARCH_HAVE_NMI_SAFE_CMPXCHG
diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index de234e7a8962..60a4ec22d849 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -154,3 +154,10 @@ static void via_no_dac(struct pci_dev *dev)
 DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_VENDOR_ID_VIA, PCI_ANY_ID,
 				PCI_CLASS_BRIDGE_PCI, 8, via_no_dac);
 #endif
+
+#ifdef CONFIG_ARCH_HAS_TEARDOWN_DMA_OPS
+void arch_teardown_dma_ops(struct device *dev)
+{
+	set_dma_ops(dev, NULL);
+}
+#endif
-- 
2.31.1