Clearing very big IOMMU tables can trigger soft lockups. This adds
cond_resched() for every million TCE updates.
The testcase is POWER9 box with 264GB guest, 4 VFIO devices from
independent IOMMU groups, 64K IOMMU pages. This configuration produces
4325376 TCE entries, each entry update incurs 4 OPAL calls to update
an individual PE TCE cache. Reducing table size to 4194304 (i.e. 256GB
guest) or removing one of 4 VFIO devices makes the problem go away so
doing cond_resched() after every million TCE updates seems sufficient.
Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
---
drivers/vfio/vfio_iommu_spapr_tce.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
index 63112c36ab2d..be3839ea3150 100644
--- a/drivers/vfio/vfio_iommu_spapr_tce.c
+++ b/drivers/vfio/vfio_iommu_spapr_tce.c
@@ -502,11 +502,15 @@ static int tce_iommu_clear(struct tce_container *container,
struct iommu_table *tbl,
unsigned long entry, unsigned long pages)
{
- unsigned long oldhpa;
+ unsigned long oldhpa, n;
long ret;
enum dma_data_direction direction;
- for ( ; pages; --pages, ++entry) {
+ for (n = 0; pages; --pages, ++entry, ++n) {
+
+ if (n && (n % 1000000 == 0))
+ cond_resched();
+
direction = DMA_NONE;
oldhpa = 0;
ret = iommu_tce_xchg(tbl, entry, &oldhpa, &direction);
--
2.11.0
