Re: [PATCH v6 19/25] iommu/arm-smmu-v3: Add support for Hardware Translation Table Update

Jean-Philippe Brucker
2020-05-04T16:36:08Z

Hi,

On Mon, May 04, 2020 at 07:54:03PM +0530, Prabhakar Kushwaha wrote:
> Dear Jean,
>
> On Thu, Apr 30, 2020 at 8:11 PM Jean-Philippe Brucker
> <jean-philippe@linaro.org> wrote:
> >
> > If the SMMU supports it and the kernel was built with HTTU support, enable
>
> is there any framework/config for HTTU which must be enabled to use this patch?
>
>
> > 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.
> >
> I believe, this statement is valid in context of this patch-set only.
>
> One cannot use code snipped to test HTTU because exiting
> io-pgtable-arm.c driver doesn't have framework to leverage HTTU
> benfits. It by-default sets AF=1 and does not set DBM.

Right, this patch only sets the hardware access and dirty flags for SVA
(page tables shared with the CPU through iommu_bind*()), it doesn't enable
anything for iommu_map/unmap(). Although I remember discussing it for VM
migration, I don't know of any effort to use hardware access/dirty bits
outside of SVA.

Thanks,
Jean