On 2021-03-30 02:22, chenxiang (M) wrote:
Hi Will,
在 2021/3/29 22:45, Will Deacon 写道:
On Sat, Mar 27, 2021 at 02:23:10PM +0800, chenxiang wrote:
From: Xiang Chen <chenxian...@hisilicon.com>
Currently it will send a iotlb sync at end of iommu unmap even if
iotlb_gather is not valid (iotlb_gather->pgsize = 0). Actually it is not
necessary, so add a check to avoid invalid iotlb sync.
Signed-off-by: Xiang Chen <chenxian...@hisilicon.com>
---
include/linux/iommu.h | 3 +++
1 file changed, 3 insertions(+)
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 9ca6e6b..6afa61b 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -529,6 +529,9 @@ static inline void iommu_flush_iotlb_all(struct
iommu_domain *domain)
static inline void iommu_iotlb_sync(struct iommu_domain *domain,
struct iommu_iotlb_gather *iotlb_gather)
{
+ if (!iotlb_gather->pgsize)
+ return;
In which circumstances does this occur?
Will
When iommu_unmap, it initializes iotlb_gather (then iotlb_gather->pgsize
= 0).
If the unmap size = ARM_LPAE_BLOCK_SIZE(lvl) && iopte_leaf(), it will
fill the iotlb_gather (set iotlb_gather->pgsize = granule);
but if the unmap size = ARM_LPAE_BLOCK_SIZE(lvl) && !iopte_leaf() (tlb
flush walk situation), iotlb_gather is not filled (iotlb_gather->pgsize
= 0),
it will still send iommu_iotlb_sync(domain, &iotlb_gather) which is
actually invalid iotlb sync at last.
I guess this can happen in DMA API usage if we've previously mapped a
block's worth of scatterlist pages into a block-=sized IOVA region, but
this is not the place to do anything about it. The main thing this patch
will do is break all the other drivers that implement .iotlb_sync but do
not use iotlb_gather.
By all means optimise SMMUv3's sync behaviour, but the only valid place
to do that is in SMMUv3's own sync callback. These particular details
are beyond what the IOMMU core knows about.
Robin.
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