On 14/08/2019 18:56, Will Deacon wrote:
Commit b6b65ca20bc9 ("iommu/io-pgtable-arm: Add support for non-strict
mode") added an unconditional call to io_pgtable_tlb_sync() immediately
after the case where we replace a block entry with a table entry during
an unmap() call. This is redundant, since the IOMMU API will call
iommu_tlb_sync() on this path and the patch in question mentions this:
| To save having to reason about it too much, make sure the invalidation
| in arm_lpae_split_blk_unmap() just performs its own unconditional sync
| to minimise the window in which we're technically violating the break-
| before-make requirement on a live mapping. This might work out redundant
| with an outer-level sync for strict unmaps, but we'll never be splitting
| blocks on a DMA fastpath anyway.
However, this sync gets in the way of deferred TLB invalidation for leaf
entries and is at best a questionable, unproven hack. Remove it.
Hey, that's my questionable, unproven hack! :P
It's not entirely clear to me how this gets in the way though - AFAICS
the intent of tlb_flush_leaf exactly matches the desired operation here,
so couldn't these just wait to be converted in patch #8?
In principle the concern is that if the caller splits a block with
iommu_unmap_fast(), there's no guarantee of seeing an iommu_tlb_sync()
before returning to the caller, and thus there's the potential to run
into a TLB conflict on a subsequent access even if the endpoint was
"good" and didn't make any accesses *during* the unmap call.
Robin.
Signed-off-by: Will Deacon <[email protected]>
---
drivers/iommu/io-pgtable-arm-v7s.c | 1 -
drivers/iommu/io-pgtable-arm.c | 1 -
2 files changed, 2 deletions(-)
diff --git a/drivers/iommu/io-pgtable-arm-v7s.c
b/drivers/iommu/io-pgtable-arm-v7s.c
index 0fc8dfab2abf..a62733c6a632 100644
--- a/drivers/iommu/io-pgtable-arm-v7s.c
+++ b/drivers/iommu/io-pgtable-arm-v7s.c
@@ -587,7 +587,6 @@ static size_t arm_v7s_split_blk_unmap(struct
arm_v7s_io_pgtable *data,
}
io_pgtable_tlb_add_flush(&data->iop, iova, size, size, true);
- io_pgtable_tlb_sync(&data->iop);
return size;
}
diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index 161a7d56264d..0d6633921c1e 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -583,7 +583,6 @@ static size_t arm_lpae_split_blk_unmap(struct
arm_lpae_io_pgtable *data,
tablep = iopte_deref(pte, data);
} else if (unmap_idx >= 0) {
io_pgtable_tlb_add_flush(&data->iop, iova, size, size, true);
- io_pgtable_tlb_sync(&data->iop);
return size;
}
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