Please backport 9e249c484128 ("iommu/amd: serialize sequence allocation under concurrent TLB invalidations") to 6.12.y

Please backport 9e249c484128 ("iommu/amd: serialize sequence allocation under concurrent TLB invalidations") to 6.12.y

[Salvatore Bonaccorso]

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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

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From c1eddc8c4ee7dc0ef651d87c51676fe4cd60a9df Mon Sep 17 00:00:00 2001
From: Uros Bizjak <ubizjak@gmail.com>
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 <ubizjak@gmail.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Cc: Will Deacon <will@kernel.org>
Cc: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20241007084356.47799-1-ubizjak@gmail.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Salvatore Bonaccorso <carnil@debian.org>
---
 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


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From c0e5ddae730cd75b2c806655a8ced16148bafa2c Mon Sep 17 00:00:00 2001
From: Ankit Soni <Ankit.Soni@amd.com>
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 <sraithal@amd.com>
Reported-by: Srikanth Aithal <sraithal@amd.com>
Signed-off-by: Ankit Soni <Ankit.Soni@amd.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
[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 <carnil@debian.org>
---
 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

Re: Please backport 9e249c484128 ("iommu/amd: serialize sequence allocation under concurrent TLB invalidations") to 6.12.y

[Sasha Levin]

> 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.

Both patches queued for 6.12.y.

I extended the same backport to 6.6.y as well - it carries d2a0cac10597
and the same older atomic64_add_return(1,..) pattern, so it is exposed
to the same race.

--
Sasha