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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Oct 29, 2018 at 01:29:28PM +0000, Paul Durrant wrote:
> The P2M code currently contains many loops to deal with the fact that,
> while it may be require to handle page orders greater than 4k, the
> IOMMU map and unmap functions do not.
> This patch adds a page_order parameter to those functions and implements
> the necessary loops within. This allows the P2M code to be substantially
> simplified.
> 
> NOTE: This patch does not modify the underlying vendor IOMMU
>       implementations to deal with page orders of more than 4k.

I'm wondering if it would make sense to drop the _page suffix from
those functions now that they take an order parameter.

> diff --git a/xen/drivers/passthrough/iommu.c b/xen/drivers/passthrough/iommu.c
> index 8b438ae4bc..e02dcb101f 100644
> --- 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)));

I would consider using IS_ALIGNED for clarity.

> +
> +    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--)

Missing spaces in the condition.

> +            /* assign to something to avoid compiler warning */
> +            ignored = hd->platform_ops->unmap_page(d, dfn_add(dfn, i));

You could likely declare ignored here to further limit it's scope?

>  
>          if ( !is_hardware_domain(d) )
>              domain_crash(d);
> +
> +        return err;

I might prefer to keep the global rc variable here and just break on
error, also keeping the 'return rc' below as it was. But that's just a
question of taste IMO.

Thanks, Roger.

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