Re: [Xen-devel] [PATCH 34/34] RFC x86: introduce directio virt cap

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Aug 21, 2018 at 05:52:39AM -0600, Jan Beulich wrote:
> >>> On 17.08.18 at 17:12, <wei.liu2@xxxxxxxxxx> wrote:
> > --- a/xen/arch/x86/sysctl.c
> > +++ b/xen/arch/x86/sysctl.c
> > @@ -92,8 +92,10 @@ void arch_do_physinfo(struct xen_sysctl_physinfo *pi)
> >             min(sizeof(pi->hw_cap), sizeof(boot_cpu_data.x86_capability)));
> >      if ( hvm_enabled )
> >          pi->capabilities |= XEN_SYSCTL_PHYSCAP_hvm;
> > -    if ( iommu_enabled )
> > +    if ( hvm_enabled && iommu_enabled )
> >          pi->capabilities |= XEN_SYSCTL_PHYSCAP_hvm_directio;
> > +    else if ( iommu_enabled )
> > +        pi->capabilities |= XEN_SYSCTL_PHYSCAP_directio;
> >  }
> 
> At the sysctl layer I think you can, as suggested iirc by Roger,
> simply replace hvm_directio with directio (or iommu). For the
> "xl info" output, otoh, I'm afraid this doesn't hold, as people
> may parse for the string. Depending on how this would best
> be addressed in the tool stack, replacing the sysctl names may
> then no longer be the most suitable solution.

In that case what do you think about the two flags this patch provides
on the toolstack level?

Essentially we change slightly hvm_directio's meaning to mean "hvm &&
iommu_enabled" while it previously mean "iommu_enabled", and then in the
absence of hvm_directio, add "directio" as an indication for
"iommu_enabled".

Wei.

> 
> Jan
> 
> 

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