Re: [RFC PATCH 6/7] iommu/amd: Introduce amd_iommu_pgtable command-line option

[Suravee Suthikulpanit]

Joerg,

On 3/18/21 10:33 PM, Joerg Roedel wrote:
> On Fri, Mar 12, 2021 at 03:04:10AM -0600, Suravee Suthikulpanit wrote:
> > To allow specification whether to use v1 or v2 IOMMU pagetable for
> > DMA remapping when calling kernel DMA-API.
> >
> > Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> > ---
> >   Documentation/admin-guide/kernel-parameters.txt |  6 ++++++
> >   drivers/iommu/amd/init.c                        | 15 +++++++++++++++
> >   2 files changed, 21 insertions(+)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 04545725f187..466e807369ea 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -319,6 +319,12 @@
> >   			             This mode requires kvm-amd.avic=1.
> >   			             (Default when IOMMU HW support is present.)
> >   
> > +	amd_iommu_pgtable= [HW,X86-64]
> > +			Specifies one of the following AMD IOMMU page table to
> > +			be used for DMA remapping for DMA-API:
> > +			v1         - Use v1 page table (Default)
> > +			v2         - Use v2 page table
>
> Any reason v2 can not be the default when it is supported by the IOMMU?

Eventually, we should be able to default to v2. However, we will need to make sure that
the v2 implementation will have comparable performance as currently used v1.

FYI: I'm also looking into adding support for SVA as well.

Thanks,
Suravee