RE: [RFC v2 03/22] intel_iommu: modify x-scalable-mode to be string option

[Liu, Yi L]

> From: Peter Xu [mailto:address@hidden]
> Sent: Friday, November 1, 2019 10:58 PM
> To: Liu, Yi L <address@hidden>
> Subject: Re: [RFC v2 03/22] intel_iommu: modify x-scalable-mode to be string 
> option
> 
> On Thu, Oct 24, 2019 at 08:34:24AM -0400, Liu Yi L wrote:
> > Intel VT-d 3.0 introduces scalable mode, and it has a bunch of
> > capabilities related to scalable mode translation, thus there are multiple
> combinations.
> > While this vIOMMU implementation wants simplify it for user by
> > providing typical combinations. User could config it by
> > "x-scalable-mode" option. The usage is as below:
> >
> > "-device intel-iommu,x-scalable-mode=["legacy"|"modern"]"
> >
> >  - "legacy": gives support for SL page table
> >  - "modern": gives support for FL page table, pasid, virtual command
> >  -  if not configured, means no scalable mode support, if not proper
> >     configured, will throw error
> >
> > Cc: Kevin Tian <address@hidden>
> > Cc: Jacob Pan <address@hidden>
> > Cc: Peter Xu <address@hidden>
> > Cc: Yi Sun <address@hidden>
> > Signed-off-by: Liu Yi L <address@hidden>
> > Signed-off-by: Yi Sun <address@hidden>
> > ---
> >  hw/i386/intel_iommu.c          | 15 +++++++++++++--
> >  hw/i386/intel_iommu_internal.h |  3 +++
> > include/hw/i386/intel_iommu.h  |  2 +-
> >  3 files changed, 17 insertions(+), 3 deletions(-)
> >
> > diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c index
> > 771bed2..4a1a07a 100644
> > --- a/hw/i386/intel_iommu.c
> > +++ b/hw/i386/intel_iommu.c
> > @@ -3019,7 +3019,7 @@ static Property vtd_properties[] = {
> >      DEFINE_PROP_UINT8("aw-bits", IntelIOMMUState, aw_bits,
> >                        VTD_HOST_ADDRESS_WIDTH),
> >      DEFINE_PROP_BOOL("caching-mode", IntelIOMMUState, caching_mode,
> FALSE),
> > -    DEFINE_PROP_BOOL("x-scalable-mode", IntelIOMMUState, scalable_mode,
> FALSE),
> > +    DEFINE_PROP_STRING("x-scalable-mode", IntelIOMMUState,
> > + scalable_mode),
> >      DEFINE_PROP_BOOL("dma-drain", IntelIOMMUState, dma_drain, true),
> >      DEFINE_PROP_END_OF_LIST(),
> >  };
> > @@ -3581,7 +3581,12 @@ static void vtd_init(IntelIOMMUState *s)
> >
> >      /* TODO: read cap/ecap from host to decide which cap to be exposed. */
> >      if (s->scalable_mode) {
> > -        s->ecap |= VTD_ECAP_SMTS | VTD_ECAP_SRS | VTD_ECAP_SLTS;
> > +        if (!strcmp(s->scalable_mode, "legacy")) {
> > +            s->ecap |= VTD_ECAP_SMTS | VTD_ECAP_SRS | VTD_ECAP_SLTS;
> > +        } else if (!strcmp(s->scalable_mode, "modern")) {
> > +            s->ecap |= VTD_ECAP_SMTS | VTD_ECAP_SRS | VTD_ECAP_PASID
> > +                       | VTD_ECAP_FLTS | VTD_ECAP_PSS;
> > +        }
> 
> Shall we do this string op only once in vtd_decide_config() then keep it 
> somewhere?

Agreed. I'll move it to vtd_decide_config().

> Something like:
> 
>   - s->scalable_mode_str to keep the string
>   - s->scalable_mode still as a bool to cache the global enablement
>   - s->scalable_modern as a bool to keep the mode
> 
> ?

So x-scalable-mode is still a string option, just to have a new field to store 
it?

> 
> These could be used in some MMIO path (I think) and parsing strings always 
> could be
> a bit overkill.

I think so. Let's just align on the direction above.

Regards,
Yi Liu