[PATCH 01/20] iommu/vt-d: Fix UCTP context table slot when copying root entries
From: Lu Baolu
Date: Mon Aug 03 2026 - 22:50:30 EST
From: Desnes Nunes <desnesn@xxxxxxxxxx>
When translation is already enabled at boot (e.g. kdump), the vt-d driver
copies context tables from the previous kernel's root table. In scalable
mode, buses that only populate the upper root half (UCTP, devfn >= 0x80)
should be written to ctxt_tbls[tbl_idx + 1] through copy_context_table().
However, the current copy path always uses tbl[tbl_idx + 0] in this situa-
tion. Since idx wraps to 0 at devfn 0x80 due to a zeroed LCTP, new_ce for
LCTP will be NULL and keep pos equals to 0. Thus, UCTP entries will be co-
pied into tbl[tbl_idx + 0] instead of tbl[tbl_idx + 1], and written after-
wards to root_entry[bus].lo instead of .hi in copy_translation_tables().
In short, devices on bus 0x80 with devfn >= 0x80 fail DMA with fault 0x39,
which will break drivers running in kernels with translation pre-enabled.
This fixes NO_PASID DMAR faults for UCTP-only buses such as:
DMAR: [DMA Read NO_PASID] Request device [80:14.0] fault addr 0xe81759000
[fault reason 0x39] SM: Present bit in Root Entry is clear
For instance, this fault yielded to locking issues between systemd and
xHCI, blocking a system's reboot after a vmcore was captured with kdump:
systemd-udevd[246]: usb3: Worker [255] processing SEQNUM=2193 is taking a long time
dracut-initqueue[277]: Timed out while waiting for udev queue to empty.
systemd-udevd[246]: usb3: Worker [255] processing SEQNUM=2193 killed
systemd-udevd[246]: usb3: Worker [255] terminated by signal 9 (KILL).
...
kdump[569]: saving vmcore complete
...
systemd-shutdown[1]: Rebooting.
INFO: task kworker/0:1:11 blocked for more than 122 seconds.
Not tainted 7.0.0-clean #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/0:1 state:D stack:0 pid:11 tgid:11 ppid:2 task_flags:0x4208160 flags:0x00080000
Workqueue: usb_hub_wq hub_event
Call Trace:
<TASK>
__schedule+0x299/0x5c0
schedule+0x27/0x80
schedule_timeout+0xbd/0x100
__wait_for_common+0x97/0x1b0
? __pfx_schedule_timeout+0x10/0x10
xhci_alloc_dev+0x9e/0x2b0
usb_alloc_dev+0x7a/0x3b0
hub_port_connect+0x285/0x960
hub_port_connect_change+0x94/0x290
port_event+0x4bb/0x840
hub_event+0x141/0x460
process_one_work+0x196/0x390
worker_thread+0x1af/0x320
? __pfx_worker_thread+0x10/0x10
kthread+0xe3/0x120
? __pfx_kthread+0x10/0x10
ret_from_fork+0x199/0x260
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1a/0x30
</TASK>
INFO: task systemd-shutdow:1 blocked for more than 122 seconds.
Not tainted 7.0.0-clean #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:systemd-shutdow state:D stack:0 pid:1 tgid:1 ppid:0 task_flags:0x400100 flags:0x00080000
Call Trace:
<TASK>
__schedule+0x299/0x5c0
schedule+0x27/0x80
schedule_preempt_disabled+0x15/0x30
__mutex_lock.constprop.0+0x547/0xac0
device_shutdown+0xac/0x1b0
kernel_restart+0x3a/0x70
__do_sys_reboot+0x147/0x240
do_syscall_64+0x11b/0x6a0
? handle_mm_fault+0x110/0x350
? do_user_addr_fault+0x206/0x680
? irqentry_exit+0x7a/0x4d0
entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7fe2958da917
RSP: 002b:00007ffc5c458618 EFLAGS: 00000206 ORIG_RAX: 00000000000000a9
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fe2958da917
RDX: 0000000001234567 RSI: 0000000028121969 RDI: 00000000fee1dead
RBP: 00007ffc5c458790 R08: 0000000000000069 R09: 00000000ffffffff
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 0000000000000000 R14: 00007ffc5c4588b8 R15: 0000000000000000
</TASK>
INFO: task systemd-shutdow:1 is blocked on a mutex likely owned by task kworker/0:1:11.
Fixes: 091d42e43d21 ("iommu/vt-d: Copy translation tables from old kernel")
Signed-off-by: Desnes Nunes <desnesn@xxxxxxxxxx>
Tested-by: Tao Liu <ltao@xxxxxxxxxx>
Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
drivers/iommu/intel/iommu.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 849d06dfe1ae..cf5f92619943 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -1446,7 +1446,7 @@ static int copy_context_table(struct intel_iommu *iommu,
struct context_entry **tbl,
int bus, bool ext)
{
- int tbl_idx, pos = 0, idx, devfn, ret = 0, did;
+ int tbl_idx, tbl_slot = 0, idx, devfn, ret = 0, did;
struct context_entry *new_ce = NULL, ce;
struct context_entry *old_ce = NULL;
struct root_entry re;
@@ -1462,10 +1462,9 @@ static int copy_context_table(struct intel_iommu *iommu,
if (idx == 0) {
/* First save what we may have and clean up */
if (new_ce) {
- tbl[tbl_idx] = new_ce;
+ tbl[tbl_idx + tbl_slot] = new_ce;
__iommu_flush_cache(iommu, new_ce,
VTD_PAGE_SIZE);
- pos = 1;
}
if (old_ce)
@@ -1487,6 +1486,9 @@ static int copy_context_table(struct intel_iommu *iommu,
}
}
+ /* Track if saving UCTP or LCTP entries in scalable mode */
+ tbl_slot = ext && devfn >= 0x80 ? 1 : 0;
+
ret = -ENOMEM;
old_ce = memremap(old_ce_phys, PAGE_SIZE,
MEMREMAP_WB);
@@ -1515,7 +1517,7 @@ static int copy_context_table(struct intel_iommu *iommu,
new_ce[idx] = ce;
}
- tbl[tbl_idx + pos] = new_ce;
+ tbl[tbl_idx + tbl_slot] = new_ce;
__iommu_flush_cache(iommu, new_ce, VTD_PAGE_SIZE);
--
2.43.0