[PATCH 6.18 396/752] iommu/amd: serialize sequence allocation under concurrent TLB invalidations

Sasha Levin
2026-02-28T17:53:39Z

From: Ankit Soni <Ankit.Soni@amd.com>

[ Upstream commit 9e249c48412828e807afddc21527eb734dc9bd3d ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.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 a698a2e7ce2a6..b0d919cd1a8fb 100644
--- a/drivers/iommu/amd/amd_iommu_types.h
+++ b/drivers/iommu/amd/amd_iommu_types.h
@@ -791,7 +791,7 @@ struct amd_iommu {

u32 flags;
volatile u64 *cmd_sem;
- atomic64_t cmd_sem_val;
+ u64 cmd_sem_val;
/*
* Track physical address to directly use it in build_completion_wait()
* and avoid adding any special checks and handling for kdump.
diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index 53afb1cb0a6fc..76efd74124b33 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -1879,7 +1879,7 @@ 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 3f2b687947dba..4beef73139611 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -1386,6 +1386,12 @@ 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
@@ -1400,11 +1406,11 @@ 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);

@@ -3086,10 +3092,11 @@ 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;
@@ -3103,7 +3110,6 @@ static void iommu_flush_irt_and_complete(struct amd_iommu *iommu, u16 devid)

out_err:
raw_spin_unlock_irqrestore(&iommu->lock, flags);
- return;
}

static inline u8 iommu_get_int_tablen(struct iommu_dev_data *dev_data)
--
2.51.0