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| author | Ankit Soni <Ankit.Soni@amd.com> | 2025-12-01 17:39:40 +0300 |
|---|---|---|
| committer | Joerg Roedel <joerg.roedel@amd.com> | 2026-01-10 12:54:38 +0300 |
| commit | d2a0cac10597068567d336e85fa3cbdbe8ca62bf (patch) | |
| tree | ddbce9e725f59690aa523a1d3290104553ab6e59 | |
| parent | 9ace4753a5202b02191d54e9fdf7f9e3d02b85eb (diff) | |
| download | linux-d2a0cac10597068567d336e85fa3cbdbe8ca62bf.tar.xz | |
iommu/amd: move wait_on_sem() out of spinlock
With iommu.strict=1, 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 <Ankit.Soni@amd.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
| -rw-r--r-- | drivers/iommu/amd/iommu.c | 25 |
1 files changed, 17 insertions, 8 deletions
diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c index 5d45795c367a..858d1669fe6c 100644 --- a/drivers/iommu/amd/iommu.c +++ b/drivers/iommu/amd/iommu.c @@ -1185,7 +1185,12 @@ static int wait_on_sem(struct amd_iommu *iommu, u64 data) { int i = 0; - while (*iommu->cmd_sem != 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 += 1; } @@ -1437,14 +1442,13 @@ static int iommu_completion_wait(struct amd_iommu *iommu) raw_spin_lock_irqsave(&iommu->lock, flags); ret = __iommu_queue_command_sync(iommu, &cmd, false); + raw_spin_unlock_irqrestore(&iommu->lock, flags); + if (ret) - goto out_unlock; + return ret; ret = wait_on_sem(iommu, data); -out_unlock: - raw_spin_unlock_irqrestore(&iommu->lock, flags); - return ret; } @@ -3121,13 +3125,18 @@ static void iommu_flush_irt_and_complete(struct amd_iommu *iommu, u16 devid) raw_spin_lock_irqsave(&iommu->lock, flags); ret = __iommu_queue_command_sync(iommu, &cmd, true); if (ret) - goto out; + goto out_err; ret = __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; } static inline u8 iommu_get_int_tablen(struct iommu_dev_data *dev_data) |