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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.10.18 at 17:56, <Paul.Durrant@xxxxxxxxxx> wrote:
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: 30 October 2018 16:08
>> 
>> >>> 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?

No, I'd prefer if you used liter 0 zero here.

>> > --- 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?

The one your patch removes elsewhere:

-                        while ( i-- )
-                            /* If statement to satisfy __must_check. */
-                            if ( iommu_unmap_page(p2m->domain,
-                                                  dfn_add(dfn, i)) )
-                                continue;

Jan


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