Re: [Xen-devel] [PATCH v2] iommu / p2m: add a page_order parameter to iommu_map/unmap_page()

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: 30 October 2018 16:08
> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxx>; Andrew Cooper
> <Andrew.Cooper3@xxxxxxxxxx>; George Dunlap <George.Dunlap@xxxxxxxxxx>; Wei
> Liu <wei.liu2@xxxxxxxxxx>; Ian Jackson <Ian.Jackson@xxxxxxxxxx>; Jun
> Nakajima <jun.nakajima@xxxxxxxxx>; Kevin Tian <kevin.tian@xxxxxxxxx>;
> Stefano Stabellini <sstabellini@xxxxxxxxxx>; xen-devel <xen-
> devel@xxxxxxxxxxxxxxxxxxxx>; Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx>; Tim (Xen.org) <tim@xxxxxxx>
> Subject: Re: [PATCH v2] iommu / p2m: add a page_order parameter to
> iommu_map/unmap_page()
> 
> >>> On 29.10.18 at 14:29, <paul.durrant@xxxxxxxxxx> wrote:
> > --- a/xen/common/grant_table.c
> > +++ b/xen/common/grant_table.c
> > @@ -1142,12 +1142,14 @@ map_grant_ref(
> >          {
> >              if ( !(kind & MAPKIND_WRITE) )
> >                  err = iommu_map_page(ld, _dfn(mfn_x(mfn)), mfn,
> > +                                     PAGE_ORDER_4K,
> >                                       IOMMUF_readable |
> IOMMUF_writable);
> >          }
> >          else if ( act_pin && !old_pin )
> >          {
> >              if ( !kind )
> >                  err = iommu_map_page(ld, _dfn(mfn_x(mfn)), mfn,
> > +                                     PAGE_ORDER_4K,
> >                                       IOMMUF_readable);
> >          }
> >          if ( err )
> > @@ -1396,10 +1398,11 @@ unmap_common(
> >
> >          kind = mapkind(lgt, rd, op->mfn);
> >          if ( !kind )
> > -            err = iommu_unmap_page(ld, _dfn(mfn_x(op->mfn)));
> > +            err = iommu_unmap_page(ld, _dfn(mfn_x(op->mfn)),
> > +                                   PAGE_ORDER_4K);
> >          else if ( !(kind & MAPKIND_WRITE) )
> >              err = iommu_map_page(ld, _dfn(mfn_x(op->mfn)), op->mfn,
> > -                                 IOMMUF_readable);
> > +                                 PAGE_ORDER_4K, IOMMUF_readable);
> >
> >          double_gt_unlock(lgt, rgt);
> 
> I am, btw, uncertain that using PAGE_ORDER_4K is correct here:
> Other than in the IOMMU code, grant table code isn't tied to a
> particular architecture, and hence ought to work fine on a port
> to an architecture with 8k, 16k, or 32k pages.

Would you suggest I add an arch specific #define for a grant table page order 
and then use that?

> 
> > --- a/xen/drivers/passthrough/iommu.c
> > +++ b/xen/drivers/passthrough/iommu.c
> > @@ -305,47 +305,76 @@ void iommu_domain_destroy(struct domain *d)
> >  }
> >
> >  int iommu_map_page(struct domain *d, dfn_t dfn, mfn_t mfn,
> > -                   unsigned int flags)
> > +                   unsigned int page_order, unsigned int flags)
> >  {
> >      const struct domain_iommu *hd = dom_iommu(d);
> > -    int rc;
> > +    unsigned long i;
> >
> >      if ( !iommu_enabled || !hd->platform_ops )
> >          return 0;
> >
> > -    rc = hd->platform_ops->map_page(d, dfn, mfn, flags);
> > -    if ( unlikely(rc) )
> > +    ASSERT(!(dfn_x(dfn) & ((1ul << page_order) - 1)));
> > +    ASSERT(!(mfn_x(mfn) & ((1ul << page_order) - 1)));
> > +
> > +    for ( i = 0; i < (1ul << page_order); i++ )
> >      {
> > +        int ignored, err = hd->platform_ops->map_page(d, dfn_add(dfn,
> i),
> > +                                                      mfn_add(mfn, i),
> > +                                                      flags);
> > +
> > +        if ( likely(!err) )
> > +            continue;
> > +
> >          if ( !d->is_shutting_down && printk_ratelimit() )
> >              printk(XENLOG_ERR
> >                     "d%d: IOMMU mapping dfn %"PRI_dfn" to mfn %"PRI_mfn"
> failed: %d\n",
> > -                   d->domain_id, dfn_x(dfn), mfn_x(mfn), rc);
> > +                   d->domain_id, dfn_x(dfn_add(dfn, i)),
> > +                   mfn_x(mfn_add(mfn, i)), err);
> > +
> > +        while (i--)
> > +            /* assign to something to avoid compiler warning */
> > +            ignored = hd->platform_ops->unmap_page(d, dfn_add(dfn, i));
> 
> Hmm, as said on v1 - please use the original mode (while-if-continue)
> here. This lets you get away without a local variable that's never
> read, and which hence future compiler versions may legitimately warn
> about.
> 

Ok, I clearly don't understand what you mean by 'while-if-continue' then. Above 
I have for-if-continue, which is what I thought you wanted. What code structure 
are you actually looking for?

  Paul

> Jan
> 


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