Re: [Xen-devel] [PATCH 1/2] VT-d: re-phrase logic in vtd_set_hwdom_mapping() for clarity

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Xen-devel [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx] On Behalf
> Of Paul Durrant
> Sent: 11 June 2018 11:35
> To: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> Cc: Kevin Tian <kevin.tian@xxxxxxxxx>; Stefano Stabellini
> <sstabellini@xxxxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>; Andrew Cooper
> <Andrew.Cooper3@xxxxxxxxxx>; Tim (Xen.org) <tim@xxxxxxx>; George
> Dunlap <George.Dunlap@xxxxxxxxxx>; Julien Grall <julien.grall@xxxxxxx>;
> Jan Beulich <jbeulich@xxxxxxxx>; Ian Jackson <Ian.Jackson@xxxxxxxxxx>;
> xen-devel@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] [PATCH 1/2] VT-d: re-phrase logic in
> vtd_set_hwdom_mapping() for clarity
> 
> > -----Original Message-----
> > From: Roger Pau Monne
> > Sent: 11 June 2018 11:31
> > To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> > Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Kevin Tian <kevin.tian@xxxxxxxxx>;
> > Stefano Stabellini <sstabellini@xxxxxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>;
> > George Dunlap <George.Dunlap@xxxxxxxxxx>; Andrew Cooper
> > <Andrew.Cooper3@xxxxxxxxxx>; Ian Jackson <Ian.Jackson@xxxxxxxxxx>; Tim
> > (Xen.org) <tim@xxxxxxx>; Julien Grall <julien.grall@xxxxxxx>; Jan Beulich
> > <jbeulich@xxxxxxxx>
> > Subject: Re: [Xen-devel] [PATCH 1/2] VT-d: re-phrase logic in
> > vtd_set_hwdom_mapping() for clarity
> >
> > On Fri, Jun 08, 2018 at 04:30:29PM +0100, Paul Durrant wrote:
> > > diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-
> > command-line.markdown
> > > index 8712a833a2..6beb28dada 100644
> > > --- a/docs/misc/xen-command-line.markdown
> > > +++ b/docs/misc/xen-command-line.markdown
> > > @@ -1212,8 +1212,8 @@ wait descriptor timed out', try increasing this
> > value.
> > >
> > >  Use this to work around firmware issues providing incorrect RMRR
> entries.
> > >  Rather than only mapping RAM pages for IOMMU accesses for Dom0,
> with
> > this
> > > -option all pages not marked as unusable in the E820 table will get a
> > mapping
> > > -established.
> > > +option all pages up to and including 4GB, not marked as unusable in the
> > > +E820 table, will get a mapping established.
> >
> > Sorry, I've reviewed the patches in the wrong order. You can ignore
> > the comments I've made related to this in patch 2.
> >
> > >  ### irq\_ratelimit (x86)
> > >  > `= <integer>`
> > > diff --git a/xen/drivers/passthrough/vtd/x86/vtd.c
> > b/xen/drivers/passthrough/vtd/x86/vtd.c
> > > index 88a60b3307..5c440ba183 100644
> > > --- a/xen/drivers/passthrough/vtd/x86/vtd.c
> > > +++ b/xen/drivers/passthrough/vtd/x86/vtd.c
> > > @@ -118,22 +118,26 @@ void __hwdom_init
> > vtd_set_hwdom_mapping(struct domain *d)
> > >
> > >      for ( i = 0; i < top; i++ )
> > >      {
> > > +        unsigned long pfn = pdx_to_pfn(i);
> > > +        bool map;
> > >          int rc = 0;
> > >
> > >          /*
> > > -         * Set up 1:1 mapping for dom0. Default to use only conventional
> RAM
> > > -         * areas and let RMRRs include needed reserved regions. When set,
> > the
> > > -         * inclusive mapping maps in everything below 4GB except unusable
> > > -         * ranges.
> > > +         * Set up 1:1 mapping for dom0. Default to include only
> > > +         * conventional RAM areas and let RMRRs include needed reserved
> > > +         * regions. When set, the inclusive mapping maps in every pfn up
> > > +         * to and including 4GB except those that fall in unusable 
> > > ranges.
> > >           */
> > > -        unsigned long pfn = pdx_to_pfn(i);
> > > +        if ( iommu_inclusive_mapping &&
> > > +             pfn <= (0xffffffffUL >> PAGE_SHIFT) )
> >
> > Please use GB(4) here for clarity.
> 
> That would be better. I left it since that's what the old code used but it 
> I'll
> change this one and the one below.

Actually since you pointed this out that my reasoning before was wrong. Because 
the comparison was with 0xffffffff >> PAGE_SHIFT (i.e. GB(4) - 1), the 
inclusive map does not include GB(4) itself... so the documentation was correct.

  Paul

> 
> >
> > > +            map = !page_is_ram_type(pfn, RAM_TYPE_UNUSABLE);
> > > +        else
> > > +            map = page_is_ram_type(pfn, RAM_TYPE_CONVENTIONAL);
> > > +
> > > +        if ( !map )
> > > +            continue;
> > >
> > > -        if ( pfn > (0xffffffffUL >> PAGE_SHIFT) ?
> > > -             (!mfn_valid(_mfn(pfn)) ||
> > > -              !page_is_ram_type(pfn, RAM_TYPE_CONVENTIONAL)) :
> > > -             iommu_inclusive_mapping ?
> > > -             page_is_ram_type(pfn, RAM_TYPE_UNUSABLE) :
> > > -             !page_is_ram_type(pfn, RAM_TYPE_CONVENTIONAL) )
> > > +        if ( pfn > (0xffffffffUL >> PAGE_SHIFT) && !mfn_valid(_mfn(pfn)) 
> > > )
> >
> > I would maybe do this check before the page_is_ram_type one, so that
> > you can discard invalid mfns earlier.
> 
> True.
> 
>   Paul
> 
> >
> > Thanks, Roger.
> 
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