Hi Jan, On 20/10/2020 14:52, Jan Beulich wrote:
While the flush coalescing optimization has been helping the non-shared case, it has actually lead to double flushes in the shared case (which ought to be the more common one nowadays at least): Once from *_set_entry() and a second time up the call tree from wherever the overriding flag gets played with. In alignment with XSA-346 suppress flushing in this case.Similarly avoid excessive setting of IOMMU_FLUSHF_added on the batched flushes: "idx" hasn't been added a new mapping for. Signed-off-by: Jan Beulich <jbeul...@suse.com> --- TBD: The Arm part really is just for completeness (and hence could also be dropped) - the affected mapping spaces aren't currently supported there.
As I may I have pointed out in the past, there are many ways to screw things up when using iommu_dont_flush_iotlb.
So I would rather not introduce any usage on Arm until we see a use-case. Cheers, -- Julien Grall
