Subject: tlbi va, vaa vs. val, vaal

From: [email-masked] (Will Deacon)
Date: Fri, 27 Feb 2015 10:24:35 +0000

On Fri, Feb 27, 2015 at 12:12:32AM +0000, Mario Smarduch wrote:
> I noticed kernel tlbflush.h use tlbi va*, vaa* variants instead of
> val, vaal ones. Reading the manual D.5.7.2 it appears that
> va*, vaa* versions invalidate intermediate caching of
> translation structures.
> 
> With stage2 enabled that may result in 20+ memory lookups
> for a 4 level page table walk. That's assuming that intermediate
> caching structures cache mappings from stage1 table entry to
> host page.

Yeah, Catalin and I discussed improving the kernel support for this,
but it requires some changes to the generic mmu_gather code so that we
can distinguish the leaf cases. I'd also like to see that done in a way
that takes into account different granule sizes (we currently iterate
over huge pages in 4k chunks). Last time I touched that, I entered a
world of pain and don't plan to return there immediately :)

Catalin -- feeling brave?

FWIW: the new IOMMU page-table stuff I just got merged *does* make use
of leaf-invalidation for the SMMU.

Will