On Tue, May 19, 2020 at 07:54:56PM +0200, Jean-Philippe Brucker wrote:

If the SMMU supports it and the kernel was built with HTTU support,
enable hardware update of access and dirty flags. This is essential for
shared page tables, to reduce the number of access faults on the fault
queue. Normal DMA with io-pgtables doesn't currently use the access or
dirty flags.

We can enable HTTU even if CPUs don't support it, because the kernel
always checks for HW dirty bit and updates the PTE flags atomically.

Signed-off-by: Jean-Philippe Brucker <redacted>
---
 drivers/iommu/arm-smmu-v3.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

How does this work if the SMMU isn't cache coherent? I'm guessing we don't
want to enable any SVA stuff in that case, but I couldn't spot where that
was being enforced. Did I just miss it?

Will