Hi
After updating to 6.12.85 in Debian we got a regression report, where
frequently a user had "AMD-Vi: Completion-Wait loop timed out" logged.
The report is at: https://bugs.debian.org/1135313
While investigating it looks d2a0cac10597 ("iommu/amd: move
wait_on_sem() out of spinlock") got backported to 6.12.y but a
followup for it not.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1135313#43 confirmed
that a backport of 9e249c484128 solved the problem. Now that one does
not apply cleanly. As an alternative the following two might work, the
first is a clean cherry-pick, the second on top needed a slight
adjustment since in 6.12.y f32fe7cb0198 is not present.
it would be though ideal if the maintainers can confirm this is the
way to go.
Regards,
Salvatore
>From c1eddc8c4ee7dc0ef651d87c51676fe4cd60a9df Mon Sep 17 00:00:00 2001
From: Uros Bizjak <[email protected]>
Date: Mon, 7 Oct 2024 10:43:31 +0200
Subject: [PATCH 1/2] iommu/amd: Use atomic64_inc_return() in iommu.c
commit 5ce73c524f5fb5abd7b1bfed0115474b4fb437b4 upstream.
Use atomic64_inc_return(&ref) instead of atomic64_add_return(1, &ref)
to use optimized implementation and ease register pressure around
the primitive for targets that implement optimized variant.
Signed-off-by: Uros Bizjak <[email protected]>
Cc: Joerg Roedel <[email protected]>
Cc: Suravee Suthikulpanit <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Robin Murphy <[email protected]>
Reviewed-by: Jason Gunthorpe <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Joerg Roedel <[email protected]>
Signed-off-by: Salvatore Bonaccorso <[email protected]>
---
drivers/iommu/amd/iommu.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index fecca5c32e8a..24e2de90ac2e 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -1266,7 +1266,7 @@ static int iommu_completion_wait(struct amd_iommu *iommu)
if (!iommu->need_sync)
return 0;
- data = atomic64_add_return(1, &iommu->cmd_sem_val);
+ data = atomic64_inc_return(&iommu->cmd_sem_val);
build_completion_wait(&cmd, iommu, data);
raw_spin_lock_irqsave(&iommu->lock, flags);
@@ -2929,7 +2929,7 @@ static void iommu_flush_irt_and_complete(struct amd_iommu *iommu, u16 devid)
return;
build_inv_irt(&cmd, devid);
- data = atomic64_add_return(1, &iommu->cmd_sem_val);
+ data = atomic64_inc_return(&iommu->cmd_sem_val);
build_completion_wait(&cmd2, iommu, data);
raw_spin_lock_irqsave(&iommu->lock, flags);
--
2.53.0
>From c0e5ddae730cd75b2c806655a8ced16148bafa2c Mon Sep 17 00:00:00 2001
From: Ankit Soni <[email protected]>
Date: Thu, 22 Jan 2026 15:30:38 +0000
Subject: [PATCH 2/2] iommu/amd: serialize sequence allocation under concurrent
TLB invalidations
commit 9e249c48412828e807afddc21527eb734dc9bd3d upstream.
With concurrent TLB invalidations, completion wait randomly gets timed out
because cmd_sem_val was incremented outside the IOMMU spinlock, allowing
CMD_COMPL_WAIT commands to be queued out of sequence and breaking the
ordering assumption in wait_on_sem().
Move the cmd_sem_val increment under iommu->lock so completion sequence
allocation is serialized with command queuing.
And remove the unnecessary return.
Fixes: d2a0cac10597 ("iommu/amd: move wait_on_sem() out of spinlock")
Tested-by: Srikanth Aithal <[email protected]>
Reported-by: Srikanth Aithal <[email protected]>
Signed-off-by: Ankit Soni <[email protected]>
Reviewed-by: Vasant Hegde <[email protected]>
Signed-off-by: Joerg Roedel <[email protected]>
[Salvatore Bonaccorso: Backport to v6.12.y where f32fe7cb0198
("iommu/amd: Add support to remap/unmap IOMMU buffers for kdump") is not
present]
Signed-off-by: Salvatore Bonaccorso <[email protected]>
---
drivers/iommu/amd/amd_iommu_types.h | 2 +-
drivers/iommu/amd/init.c | 2 +-
drivers/iommu/amd/iommu.c | 18 ++++++++++++------
3 files changed, 14 insertions(+), 8 deletions(-)
diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h
index a14ee649d3da..df2aa1c4fafc 100644
--- a/drivers/iommu/amd/amd_iommu_types.h
+++ b/drivers/iommu/amd/amd_iommu_types.h
@@ -781,7 +781,7 @@ struct amd_iommu {
u32 flags;
volatile u64 *cmd_sem;
- atomic64_t cmd_sem_val;
+ u64 cmd_sem_val;
#ifdef CONFIG_AMD_IOMMU_DEBUGFS
/* DebugFS Info */
diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index e1816ae8699d..78e9ceda2338 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -1742,7 +1742,7 @@ static int __init init_iommu_one(struct amd_iommu *iommu, struct ivhd_header *h,
iommu->pci_seg = pci_seg;
raw_spin_lock_init(&iommu->lock);
- atomic64_set(&iommu->cmd_sem_val, 0);
+ iommu->cmd_sem_val = 0;
/* Add IOMMU to internal data structures */
list_add_tail(&iommu->list, &amd_iommu_list);
diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index 24e2de90ac2e..d0e53a03eff0 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -1252,6 +1252,12 @@ static int iommu_queue_command(struct amd_iommu *iommu, struct iommu_cmd *cmd)
return iommu_queue_command_sync(iommu, cmd, true);
}
+static u64 get_cmdsem_val(struct amd_iommu *iommu)
+{
+ lockdep_assert_held(&iommu->lock);
+ return ++iommu->cmd_sem_val;
+}
+
/*
* This function queues a completion wait command into the command
* buffer of an IOMMU
@@ -1266,11 +1272,11 @@ static int iommu_completion_wait(struct amd_iommu *iommu)
if (!iommu->need_sync)
return 0;
- data = atomic64_inc_return(&iommu->cmd_sem_val);
- build_completion_wait(&cmd, iommu, data);
-
raw_spin_lock_irqsave(&iommu->lock, flags);
+ data = get_cmdsem_val(iommu);
+ build_completion_wait(&cmd, iommu, data);
+
ret = __iommu_queue_command_sync(iommu, &cmd, false);
raw_spin_unlock_irqrestore(&iommu->lock, flags);
@@ -2929,10 +2935,11 @@ static void iommu_flush_irt_and_complete(struct amd_iommu *iommu, u16 devid)
return;
build_inv_irt(&cmd, devid);
- data = atomic64_inc_return(&iommu->cmd_sem_val);
- build_completion_wait(&cmd2, iommu, data);
raw_spin_lock_irqsave(&iommu->lock, flags);
+ data = get_cmdsem_val(iommu);
+ build_completion_wait(&cmd2, iommu, data);
+
ret = __iommu_queue_command_sync(iommu, &cmd, true);
if (ret)
goto out_err;
@@ -2946,7 +2953,6 @@ static void iommu_flush_irt_and_complete(struct amd_iommu *iommu, u16 devid)
out_err:
raw_spin_unlock_irqrestore(&iommu->lock, flags);
- return;
}
static void set_dte_irq_entry(struct amd_iommu *iommu, u16 devid,
--
2.53.0
