Re: [PATCH v6 06/18] iommu/vt-d: Implement device and iommu preserve/unpreserve ops

[Samiullah Khawaja <skhawaja@google.com>]

On Wed, Oct 28, 2026 at 09:51:18AM +0800, Baolu Lu wrote:
>On 10/25/26 10:19, Samiullah Khawaja wrote:
>>Add implementation of the device and iommu preservation in a separate
>>file. Also set the device and iommu preserve/unpreserve ops in the
>>struct iommu_ops.
>>
>>Preservation is refused for devices where ATS is supported. Carrying an
>>active ATS configuration across kexec would require adopting the ATS
>>state in the PCI core and in the context entries, and handling the
>>disable-to-enable, enable-to-disable and STU mismatch cases for a live
>>device.
>>
>>Note that the preserved iommu root table, context table and device pasid
>>table will need cleanup as devices do not go through the release flow
>>during kexec. So the stale entries need to be removed during shutdown.
>>This is done in the next commit.
>>
>>Signed-off-by: Samiullah Khawaja <skhawaja@google.com>
>>---
>>  MAINTAINERS                      |   8 +
>>  drivers/iommu/intel/Makefile     |   1 +
>>  drivers/iommu/intel/iommu.c      |   9 +-
>>  drivers/iommu/intel/iommu.h      |  13 ++
>>  drivers/iommu/intel/liveupdate.c | 246 +++++++++++++++++++++++++++++++
>>  include/linux/kho/abi/iommu.h    |  27 ++++
>>  6 files changed, 302 insertions(+), 2 deletions(-)
>>  create mode 100644 drivers/iommu/intel/liveupdate.c
>>

[snip]

>>+
>>+static int preserve_iommu_context_tables(struct device_domain_info *info)
>>+{
>>+	struct iommu_hw_ser *iommu_ser;
>>+	struct intel_iommu *iommu;
>>+	int ret;
>>+	int i;
>>+
>>+	/* IOMMU for this device should already preserved.*/
>
>... should already be preserved ...

I will fix this in the next revision.
>
>>+	iommu = info->iommu;
>>+	iommu_ser = iommu_preserved_state(&iommu->iommu);
>>+	if (!iommu_ser)
>>+		return -EINVAL;
>>+
>>+	/*
>>+	 * We could do preservation of context tables only for the bus of this
>>+	 * device, but these devices can have PCI aliases, so context tables for
>>+	 * those will also require preservation. Also unpreserve would require
>>+	 * some kind of refcounting where the context table will only be
>>+	 * unpreserved when the last device associated with it is unpreserved.
>>+	 *
>>+	 * This introduces unnecessary complication with minimum benefits as the
>>+	 * unpreserved context tables will probably be recreated by the next
>>+	 * kernel as these are all active devices. We follow simpler approach by
>>+	 * just preserving the currently active context tables.
>>+	 */
>>+	for (i = 0; i < ROOT_ENTRY_NR; i++) {
>>+		ret = preserve_context_table(iommu, iommu_ser, i, 0);
>>+		if (ret)
>>+			return ret;
>>+
>>+		if (!sm_supported(iommu))
>>+			continue;
>>+
>>+		ret = preserve_context_table(iommu, iommu_ser, i, 0x80);
>>+		if (ret)
>>+			return ret;
>>+	}
>>+
>>+	return 0;
>>+}
>>+
>>+

[snip]

>>+/**
>>+ * struct iommu_intel_ser - Serialized state of an Intel IOMMU instance
>>+ * @features: Bitmask of Intel IOMMU specific features
>>+ * @sm_enabled: Whether the IOMMU was used in scalable mode
>>+ * @phys_addr: Physical address of the IOMMU register base
>>+ * @root_table: Physical address of the root entry table
>>+ * @context_tables_bitmap: Bitmap representing the context tables that are
>>+ * preserved.
>>+ */
>>+struct iommu_intel_ser {
>>+	u32 features;
>>+	u8 sm_enabled;
>>+	u8 padding[3];
>>+	u64 phys_addr;
>>+	u64 root_table;
>>+	u64 context_tables_bitmap[VTD_PRESERVED_BITMAP_LONGS];
>>+} __packed;
>>+
>>  /**
>>   * struct iommu_hw_ser - Serialized state of an IOMMU instance
>>   * @hdr: Common object header
>>   * @token: Unique token to identify the IOMMU instance
>>   * @type: IOMMU type serialized state belongs to
>>   * @reserved: Reserved for future common fields.
>>+ * @intel: Intel specific serialization data
>>   */
>>  struct iommu_hw_ser {
>>  	struct iommu_hdr_ser hdr;
>>  	u64 token;
>>  	u64 type;
>>  	u64 reserved[2];
>>+	union {
>>+		struct iommu_intel_ser intel;
>>+	};
>>  } __packed;
>>  /**
>
>This patch looks good to me,
>
>Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>

Thanks for the review,
Sami