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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Dec 2025 14:39:57.0685 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: c3a91075-b2fd-4772-314b-08de30e77fb4 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CH2PEPF0000013F.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA0PR12MB7601 Content-Type: text/plain; charset="utf-8" With iommu.strict=3D1, the existing completion wait path can cause soft lockups under stressed environment, as wait_on_sem() busy-waits under the spinlock with interrupts disabled. Move the completion wait in iommu_completion_wait() out of the spinlock. wait_on_sem() only polls the hardware-updated cmd_sem and does not require iommu->lock, so holding the lock during the busy wait unnecessarily increases contention and extends the time with interrupts disabled. Signed-off-by: Ankit Soni --- drivers/iommu/amd/iommu.c | 25 +++++++++++++++++-------- 1 file changed, 17 insertions(+), 8 deletions(-) diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c index 2e1865daa1ce..3ef188b39bf8 100644 --- a/drivers/iommu/amd/iommu.c +++ b/drivers/iommu/amd/iommu.c @@ -1161,7 +1161,12 @@ static int wait_on_sem(struct amd_iommu *iommu, u64 = data) { int i =3D 0; =20 - while (*iommu->cmd_sem !=3D data && i < LOOP_TIMEOUT) { + /* + * cmd_sem holds a monotonically non-decreasing completion sequence + * number. + */ + while ((__s64)(READ_ONCE(*iommu->cmd_sem) - data) < 0 && + i < LOOP_TIMEOUT) { udelay(1); i +=3D 1; } @@ -1406,14 +1411,13 @@ static int iommu_completion_wait(struct amd_iommu *= iommu) raw_spin_lock_irqsave(&iommu->lock, flags); =20 ret =3D __iommu_queue_command_sync(iommu, &cmd, false); + raw_spin_unlock_irqrestore(&iommu->lock, flags); + if (ret) - goto out_unlock; + return ret; =20 ret =3D wait_on_sem(iommu, data); =20 -out_unlock: - raw_spin_unlock_irqrestore(&iommu->lock, flags); - return ret; } =20 @@ -3094,13 +3098,18 @@ static void iommu_flush_irt_and_complete(struct amd= _iommu *iommu, u16 devid) raw_spin_lock_irqsave(&iommu->lock, flags); ret =3D __iommu_queue_command_sync(iommu, &cmd, true); if (ret) - goto out; + goto out_err; ret =3D __iommu_queue_command_sync(iommu, &cmd2, false); if (ret) - goto out; + goto out_err; + raw_spin_unlock_irqrestore(&iommu->lock, flags); + wait_on_sem(iommu, data); -out: + return; + +out_err: raw_spin_unlock_irqrestore(&iommu->lock, flags); + return; } =20 static inline u8 iommu_get_int_tablen(struct iommu_dev_data *dev_data) --=20 2.43.0