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

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

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.

> +            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.

Thanks, Roger.

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