Re: [Xen-devel] [PATCH v3 1/2] VT-d: re-phrase logic in vtd_set_hwdom_mapping() for clarity

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Paul Durrant [mailto:paul.durrant@xxxxxxxxxx]
> Sent: Saturday, June 16, 2018 12:31 AM
> 
> It is hard to reconcile the comment at the top of the loop in
> vtd_set_hwdom_mapping() with the if statement following it. This patch
> re-phrases the logic, preserving the semantics, but making it easier
> to read.
> 
> The patch also modifies the Xen command line documentation to make it
> clear that iommu_inclusive_mapping only applies to pages up to the 4GB
> boundary.
> 
> NOTE: This patch also corrects the indentation of the printk() towards
>       the end of vtd_set_hwdom_mapping().
> 
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> Reviewed-by: Roger Pau Monne <roger.pau@xxxxxxxxxx>

Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>, with one small comment
below

> ---
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Tim Deegan <tim@xxxxxxx>
> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
> 
> v3:
>  - Fix top calculation by introducing max_pfn.
>  - Move comment.
> 
> v2:
>  - Compare against GB(4) rather than 0xffffffff.
> ---
>  docs/misc/xen-command-line.markdown   |  4 ++--
>  xen/drivers/passthrough/vtd/x86/vtd.c | 34 +++++++++++++++++++---------
> ------
>  2 files changed, 21 insertions(+), 17 deletions(-)
> 
> diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-
> command-line.markdown
> index 8712a833a2..b75471b51a 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 4GB, not marked as unusable in the E820 table, will
> +get a mapping established.
> 
>  ### irq\_ratelimit (x86)
>  > `= <integer>`
> diff --git a/xen/drivers/passthrough/vtd/x86/vtd.c
> b/xen/drivers/passthrough/vtd/x86/vtd.c
> index 88a60b3307..6551f01e31 100644
> --- a/xen/drivers/passthrough/vtd/x86/vtd.c
> +++ b/xen/drivers/passthrough/vtd/x86/vtd.c
> @@ -110,30 +110,34 @@ void hvm_dpci_isairq_eoi(struct domain *d,
> unsigned int isairq)
> 
>  void __hwdom_init vtd_set_hwdom_mapping(struct domain *d)
>  {
> -    unsigned long i, j, tmp, top;
> +    unsigned long i, j, tmp, top, max_pfn;
> 
>      BUG_ON(!is_hardware_domain(d));
> 
> -    top = max(max_pdx, pfn_to_pdx(0xffffffffUL >> PAGE_SHIFT) + 1);
> +    max_pfn = (GB(4) >> PAGE_SHIFT) - 1;
> +    top = max(max_pdx, pfn_to_pdx(max_pfn) + 1);
> 
>      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 4GB except those that fall in unusable ranges.
>           */

I'm not sure whether others feel same as me. I read the last sentence
as if 'inclusive mapping' ONLY maps <4GB frames while leaving >=4GB
frames unmapped. If it is the case, adding a 'further' i.e. "the inclusive
mapping further maps" sounds more clear?

> -        unsigned long pfn = pdx_to_pfn(i);
> +        if ( pfn > max_pfn && !mfn_valid(_mfn(pfn)) )
> +            continue;
> +
> +        if ( iommu_inclusive_mapping && pfn <= max_pfn )
> +            map = !page_is_ram_type(pfn, RAM_TYPE_UNUSABLE);
> +        else
> +            map = page_is_ram_type(pfn, RAM_TYPE_CONVENTIONAL);
> 
> -        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 ( !map )
>              continue;
> 
>          /* Exclude Xen bits */
> @@ -151,8 +155,8 @@ void __hwdom_init
> vtd_set_hwdom_mapping(struct domain *d)
>          }
> 
>          if ( rc )
> -           printk(XENLOG_WARNING VTDPREFIX " d%d: IOMMU mapping
> failed: %d\n",
> -                  d->domain_id, rc);
> +            printk(XENLOG_WARNING VTDPREFIX " d%d: IOMMU mapping
> failed: %d\n",
> +                   d->domain_id, rc);
> 
>          if (!(i & (0xfffff >> (PAGE_SHIFT - PAGE_SHIFT_4K))))
>              process_pending_softirqs();
> --
> 2.11.0


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