Re: [Xen-devel] [PATCH v2 3/4] xen/dom0: Drop iommu_hwdom_inclusive entirely

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

On Mon, Dec 31, 2018 at 03:16:22PM +0000, Andrew Cooper wrote:
> This option is unique to x86 PV dom0's, but it is not sensible to have a
> catch-all which blindly maps all non-RAM regions into the IOMMU.
> 
> The map-reserved option remains, and covers all the buggy firmware issues that
> I am aware of.  The two common cases are legacy USB keyboard emulation, and
> the BMC mailbox used by vendor firmware in NICs/HBAs to report information
> back to the iLO/iDRAC/etc for remote remote management purposes.
> 
> A specific advantage of removing this option is that x86 dom0's IOMMU setup is
> now consistent between PV and PVH.
> 
> This removal is not expected to have any impact, due to map-reserved
> remaining.  In the unlikely case that it does cause an issue, we should
> introduce other map-$SPECIFIC options rather than re-introducing this
> catch-all.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Julien Grall <julien.grall@xxxxxxx>
> CC: Jun Nakajima <jun.nakajima@xxxxxxxxx>
> CC: Kevin Tian <kevin.tian@xxxxxxxxx>
> 
> v2:
>  * New
> ---
>  docs/misc/xen-command-line.markdown   | 19 +++----------------
>  xen/drivers/passthrough/arm/smmu.c    |  4 ----
>  xen/drivers/passthrough/iommu.c       |  3 ---
>  xen/drivers/passthrough/vtd/x86/vtd.c |  6 ------
>  xen/drivers/passthrough/x86/iommu.c   | 14 ++------------
>  xen/include/xen/iommu.h               |  2 +-
>  6 files changed, 6 insertions(+), 42 deletions(-)
> 
> diff --git a/docs/misc/xen-command-line.markdown 
> b/docs/misc/xen-command-line.markdown
> index 0aeb786..3a9af17 100644
> --- a/docs/misc/xen-command-line.markdown
> +++ b/docs/misc/xen-command-line.markdown
> @@ -664,8 +664,7 @@ Controls for how dom0 is constructed on x86 systems.
>      hardware is not HAP-capable.
>  
>  ### dom0-iommu
> -> `= List of [ passthrough=<bool>, strict=<bool>, map-inclusive=<bool>,
> ->              map-reserved=<bool> ]`
> +> `= List of [ passthrough=<bool>, strict=<bool>, map-reserved=<bool> ]`
>  
>  Controls for the dom0 IOMMU setup.
>  
> @@ -692,9 +691,8 @@ Controls for the dom0 IOMMU setup.
>      other domains in the system don't live in a compatible address space), 
> and
>      is ignored for ARM.
>  
> -*   The `map-inclusive` boolean is applicable to x86 PV dom0's, and sets up
> -    identity IOMMU mappings for all non-RAM regions below 4GB except for
> -    unusable ranges, and ranges belonging to Xen.
> +*   The `map-reserved` boolean is applicable to x86, and sets up identity 
> IOMMU
> +    mappings for all E820 reserved regions below 4GB.

Current code will map all reserved regions below max_pdx, but maybe
the code should be changed to only map reserved regions < 4GB?

Thanks, Roger.

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