linux-kernel - [PATCH 1/2] amd/iommu: Preserve domain ids inside the kdump kernel

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Message-ID: <20251114104442.23296-2-sarunkod@amd.com>
Date: Fri, 14 Nov 2025 16:14:41 +0530
From: Sairaj Kodilkar <sarunkod@....com>
To: <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
CC: <joro@...tes.org>, <suravee.suthikulpanit@....com>,
	<vasant.hegde@....com>, <ashish.kalra@....com>, <robin.murphy@....com>,
	<will@...nel.org>, Sairaj Kodilkar <sarunkod@....com>
Subject: [PATCH 1/2] amd/iommu: Preserve domain ids inside the kdump kernel

Currently AMD IOMMU driver does not reserve domain ids programmed in the
DTE while reusing the device table inside kdump kernel. This can cause
reallocation of these domain ids for newer domains that are created by
the kdump kernel, which can lead to potential IO_PAGE_FAULTs

Hence reserve these ids inside pdom_ids.

Fixes: 38e5f33ee359 ("iommu/amd: Reuse device table for kdump")
Signed-off-by: Sairaj Kodilkar <sarunkod@....com>
---
 drivers/iommu/amd/init.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index f2991c11867c..9375fba1071c 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -1136,9 +1136,13 @@ static void set_dte_bit(struct dev_table_entry *dte, u8 bit)
 static bool __reuse_device_table(struct amd_iommu *iommu)
 {
 	struct amd_iommu_pci_seg *pci_seg = iommu->pci_seg;
-	u32 lo, hi, old_devtb_size;
+	struct dev_table_entry *old_dev_tbl_entry;
+	u32 lo, hi, old_devtb_size, devid;
 	phys_addr_t old_devtb_phys;
+	u16 dom_id;
+	bool dte_v;
 	u64 entry;
+	int ret;
 
 	/* Each IOMMU use separate device table with the same size */
 	lo = readl(iommu->mmio_base + MMIO_DEV_TABLE_OFFSET);
@@ -1173,6 +1177,25 @@ static bool __reuse_device_table(struct amd_iommu *iommu)
 		return false;
 	}
 
+	for (devid = 0; devid <= pci_seg->last_bdf; devid++) {
+		old_dev_tbl_entry = &pci_seg->old_dev_tbl_cpy[devid];
+		dte_v = old_dev_tbl_entry->data[0] & DTE_FLAG_V;
+		dom_id = old_dev_tbl_entry->data[1] & DEV_DOMID_MASK;
+
+		if (!dte_v || !dom_id)
+			continue;
+		/*
+		 * ID reseveration can fail with -ENOSPC when there
+		 * are multiple devices present in the same domain,
+		 * hence check only for -ENOMEM.
+		 */
+		ret = ida_alloc_range(&pdom_ids, dom_id, dom_id, GFP_ATOMIC);
+		if (ret == -ENOMEM) {
+			pr_err("Failed to reserve domain ID 0x%x\n", dom_id);
+			return false;
+		}
+	}
+
 	return true;
 }
 
-- 
2.34.1