From mboxrd@z Thu Jan  1 00:00:00 1970
From: Julien Grall <julien.grall@citrix.com>
Subject: Re: [PATCH 3/4 RFC] x86/p2m: use large pages for MMIO
 mappings
Date: Tue, 29 Sep 2015 12:33:20 +0100
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To: Jan Beulich <JBeulich@suse.com>, xen-devel <xen-devel@lists.xenproject.org>
Cc: Wei Liu <wei.liu2@citrix.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, George Dunlap <George.Dunlap@eu.citrix.com>, Andrew Cooper <andrew.cooper3@citrix.com>, Ian Jackson <Ian.Jackson@eu.citrix.com>, Ian Campbell <Ian.Campbell@eu.citrix.com>, Tiejun Chen <tiejun.chen@intel.com>, Malcolm Crossley <malcolm.crossley@citrix.com>, Keir Fraser <keir@xen.org>
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Hi Jan,

Sorry I hadn't much time to look at it until now.

On 15/09/15 08:34, Jan Beulich wrote:
> When mapping large BARs (e.g. the frame buffer of a graphics card) the
> overhead or establishing such mappings using onle 4k pages has,
> particularly after the XSA-125 fix, become unacceptable. Alter the
> XEN_DOMCTL_memory_mapping semantics once again, so that there's no
> longer a fixed amount of guest frames that represents the upper limit
> of what a single invocation can map. Instead bound execution time by
> limiting the number of iterations (regardless of page size).
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> ---
> RFC reasons:
> - ARM side unimplemented (and hence libxc for now made cope with both
>   models), the main issue (besides my inability to test any change
>   there) being the many internal uses of map_mmio_regions())

map_mmio_regions is used in ARM to map all the device memory in a guest.
We expect this function to map everything at once when called during
DOM0 build and/or when a guest is created (used to map the interrupt
controller).

I would rather prefer to avoid introducing specific helpers with
slightly different behavior (i.e one is only mapping N page, the other
everything).

What about extending map_mmio_regions to take a parameter telling if we
want to limit the number of mapping in a single invocation?

Regards,

-- 
Julien Grall