Re: [PATCH v2 2/5] iommu: introduce dom0-iommu option

From: Paul Durrant <Paul.Durrant@citrix.com>
To: Roger Pau Monne <roger.pau@citrix.com>
Cc: Kevin Tian <kevin.tian@intel.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
	Andrew Cooper <Andrew.Cooper3@citrix.com>,
	"Tim (Xen.org)" <tim@xen.org>,
	George Dunlap <George.Dunlap@citrix.com>,
	Julien Grall <julien.grall@arm.com>,
	Jan Beulich <JBeulich@suse.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	Ian Jackson <Ian.Jackson@citrix.com>,
	Brian Woods <brian.woods@amd.com>
Subject: Re: [PATCH v2 2/5] iommu: introduce dom0-iommu option
Date: Fri, 3 Aug 2018 09:37:34 +0000	[thread overview]
Message-ID: <3145a7d75f314682b75277201c352068@AMSPEX02CL03.citrite.net> (raw)
In-Reply-To: <20180803093239.plnbarak47r3bk6r@mac>

> -----Original Message-----
[snip]
> > The problem then is what does, say, reserved + no-inclusive mean? I guess
> we could have a flag for each non ram E820 range type?
> 
> reserved + no-inclusive would make sense for a PV Dom0 running on
> Intel hardware in order to map only the reserved regions instead of
> mapping almost everything below 4GB by default.

Ok, that makes sense.

> 
> What about the following description of the options, do you think it's
> clear enough?
> 
> > `= List of [ none | strict | relaxed | inclusive | reserved ]`
> 
> * `none`: disables DMA remapping for Dom0.
> 
> The following two options control how RAM regions are mapped in the
> iommu for
> Dom0:
> 
> * `strict`: sets up DMA remapping only for the memory Dom0 actually got
>   assigned.
> 
> * `relaxed`: sets DMA remapping for all the host RAM except regions in use
> by
>   Xen. This is the default iommu behaviour.
> 
> Note that all the above options are mutually exclusive. Specifying more than
> one on the `dom0-iommu` command line will result in undefined behavior.
> 
> The following options control whether non-RAM regions are added to the
> Dom0
> iommu tables. Note that they can be prefixed with `no-` to effect the inverse
> meaning:
> 
> * `inclusive`: sets up DMA remapping for all the non-RAM memory below
> 4GB
>   except for unusable ranges. Use this to work around firmware issues
> providing
>   incorrect RMRR/IVMD entries. Rather than only mapping RAM pages for
> IOMMU
>   accesses for Dom0, with this option all pages up to 4GB, not marked as
>   unusable in the E820 table, will get a mapping established. Note that this
>   option is only applicable to a PV Dom0 and is enabled by default on Intel
>   hardware.
> 
> * `reserved`: sets up DMA remapping for all the reserved regions in the
> memory
>   map for Dom0. Use this to work around firmware issues providing incorrect
>   RMRR or IVMD entries. Rather than only mapping RAM pages for IOMMU
> accesses
>   for Dom0, all memory regions marked as reserved in the memory map that
> don't
>   overlap with any MMIO region from emulated devices will be identity
> mapped.
>   This option maps a subset of the memory that would be mapped when
> using the
>   `inclusive` option. This option is available to a PVH Dom0 and is enabled by
>   default on Intel hardware.
> 

With that explanation, I think it is clear enough :-)

Cheers,

  Paul

> Thanks, Roger.

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel