Re: [Xen-devel] [PATCH v9 3/6] sysctl / libxl: report whether IOMMU/HAP page table sharing is supported

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: 12 September 2019 14:04
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Julien Grall <julien.grall@xxxxxxx>; 
> Andrew Cooper
> <Andrew.Cooper3@xxxxxxxxxx>; Anthony Perard <anthony.perard@xxxxxxxxxx>; 
> Christian Lindig
> <christian.lindig@xxxxxxxxxx>; George Dunlap <George.Dunlap@xxxxxxxxxx>; Ian 
> Jackson
> <Ian.Jackson@xxxxxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>; Konrad 
> Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx>; DavidScott <dave@xxxxxxxxxx>; Tim (Xen.org) 
> <tim@xxxxxxx>; Wei Liu
> <wl@xxxxxxx>
> Subject: Re: [PATCH v9 3/6] sysctl / libxl: report whether IOMMU/HAP page 
> table sharing is supported
> 
> On 12.09.2019 13:17, Paul Durrant wrote:
> > --- a/xen/arch/arm/sysctl.c
> > +++ b/xen/arch/arm/sysctl.c
> > @@ -15,6 +15,9 @@
> >  void arch_do_physinfo(struct xen_sysctl_physinfo *pi)
> >  {
> >      pi->capabilities |= XEN_SYSCTL_PHYSCAP_hvm | XEN_SYSCTL_PHYSCAP_hap;
> > +
> > +    if ( iommu_enabled && iommu_hap_pt_share )
> > +        pi->capabilities |= XEN_SYSCTL_PHYSCAP_iommu_hap_pt_share;
> >  }
> 
> I think this should be done in common code.
> 
> > --- a/xen/arch/x86/sysctl.c
> > +++ b/xen/arch/x86/sysctl.c
> > @@ -164,7 +164,12 @@ void arch_do_physinfo(struct xen_sysctl_physinfo *pi)
> >      if ( IS_ENABLED(CONFIG_PV) )
> >          pi->capabilities |= XEN_SYSCTL_PHYSCAP_pv;
> >      if ( hvm_hap_supported() )
> > +    {
> >          pi->capabilities |= XEN_SYSCTL_PHYSCAP_hap;
> > +
> > +        if ( iommu_enabled && iommu_hap_pt_share )
> > +            pi->capabilities |= XEN_SYSCTL_PHYSCAP_iommu_hap_pt_share;
> > +    }
> >  }
> 
> And if it's important to not have the bit set when !hvm_hap_supported(),

...and that's what it’s not in common code... there is no hvm_hap_supported() 
for Arm

> then iommu_hap_pt_share should be cleared in __init code in this case.

That would have been an alternative approach if you'd not wanted it #defined in 
patch #5. (Yes it's a later patch in the series, but this one is later 
chronologically and I didn't want to invalidate the other patch.)
I could perhaps implement hvm_hap_supported() for Arm?

  Paul

> 
> Jan
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