Commit d2a0cac1 authored by Ankit Soni's avatar Ankit Soni Committed by Joerg Roedel
Browse files

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: default avatarAnkit Soni <Ankit.Soni@amd.com>
Reviewed-by: default avatarVasant Hegde <vasant.hegde@amd.com>
Signed-off-by: default avatarJoerg Roedel <joerg.roedel@amd.com>
parent 9ace4753

drivers/iommu/amd/iommu.c

+17 −8
Original line number Diff line number Diff line
@@ -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)