Re: [PATCH for-5.2 v4 00/11] SMMUv3.2 Range-based TLB Invalidation Support

[Peter Maydell <peter.maydell@linaro.org>]

On Tue, 28 Jul 2020 at 16:08, Eric Auger <eric.auger@redhat.com> wrote:
>
> SMMU3.2 brings the support of range-based TLB invalidation and
> level hint. When this feature is supported, the SMMUv3 driver
> is allowed to send TLB invalidations for a range of IOVAs instead
> of using page based invalidation.
>
> Implementing this feature in the virtual SMMUv3 device is
> mandated for DPDK on guest use case: DPDK uses hugepage
> buffers and guest sends invalidations for blocks. Without
> this feature, a guest invalidation of a block of 1GB for instance
> translates into a storm of page invalidations. Each of them
> is trapped by the VMM and cascaded downto the physical IOMMU.
> This completely stalls the execution. This integration issue
> was initially reported in [1].
>
> Now SMMUv3.2 specifies additional parameters to NH_VA and NH_VAA
> stage 1 invalidation commands so we can support those extensions.
>
> Supporting block mappings in the IOTLB look sensible in terms of
> TLB entry consumption. However looking at virtio/vhost device usage,
> without block mapping and without range invalidation (< 5.7 kernels
> it may be less performant. However for recent guest kernels
> supporting range invalidations [2], the performance should be similar.

I think this is all reviewed now; I've put it on my list
of series to apply to target-arm.next in once 5.1 is out
and we reopen the trunk for 5.2.

thanks
-- PMM