Re: [PATCH v13 4/6] iommu/vt-d: Add support for IOMMU default DMA mode build options

[John Garry]

On 18/06/2021 02:46, Lu Baolu wrote:

Hi baolu,

> > I need to change that. How about this:
> >
> > bool print_warning = false;
> >
> > for_each_active_iommu(iommu, drhd) {
> >      /*
> >       * The flush queue implementation does not perform
> >       * page-selective invalidations that are required for efficient
> >       * TLB flushes in virtual environments.  The benefit of batching
> >       * is likely to be much lower than the overhead of synchronizing
> >       * the virtual and physical IOMMU page-tables.
> >       */
> >      if (!print_warning && cap_caching_mode(iommu->cap)) {
> >          pr_warn("IOMMU batching disallowed due to virtualization\n");
> >          iommu_set_dma_strict(true);
> >          print_warning = true;
> >      }
> >      ...
> > }
> >
> > or use pr_warn_once().
>
>  From my p.o.v, pr_xxxx_once() is better.
>
> How about using a pr_info_once()? I don't think it's a warning, it's
> just a policy choice in VM environment.

ok, I can go with that, which Robin mostly agrees with.

Thanks,
John