Re: [Xen-devel] [PATCH] Provide support for multiple frame buffers in Xen

[Tim Deegan <tim@xxxxxxx>]

Hi,

At 14:28 -0500 on 21 Jan (1358778509), Robert Phillips wrote:
> Support is provided for both shadow and hardware assisted paging (HAP)
> modes. This code bookkeeps the set of video frame buffers (vram),
> detects when the guest has modified any of those buffers and, upon request,
> returns a bitmap of the modified pages.
> This lets other software components re-paint the portions of the monitor
> (or monitors) that have changed.
> Each monitor has a frame buffer of some size at some position
> in guest physical memory.
> The set of frame buffers being tracked can change over time as monitors
> are plugged and unplugged.

This doesn't apply to tip of xen-unstable.  Also: 

> +        ext = __map_domain_page(pg);
> +        /* Is unmapped in dirty_vram_free() */

Mappings from map_domain_page() can't be kept around like this.  They're
supposed to be short-term, and in systems where we don't have a full 1-1
map of memory (e.g. x86 once Jan's 16TB-support series goes in) there
are a limited number of mapping slots.

Jan, what do you recommend here?  These are pages of linked-list
entries, part of the p2m/mm overhead and so allocated from the guest's
shadow memory.  Are we going to have to allocate them from xenheap
instead or is there any way to avoid that?

Tim.


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