Re: [Xen-devel] [PATCH v2 16/17] libxc/xc_dom_arm: Copy ACPI tables to guest space

[George Dunlap <dunlapg@xxxxxxxxx>]

On Thu, Jul 21, 2016 at 10:15 PM, Stefano Stabellini
<sstabellini@xxxxxxxxxx> wrote:
>> You are assuming that the guest will map the ACPI blob with the same
>> attributes as the rest of the superpage.
>>
>> IHMO, a sane operating system will want to map the ACPI blob read-only.
>
> That's true. But there are other things which might be mapped
> differently and could shatter a stage-1 superpage mapping (especially on
> x86 that has a much more complex memory map than ARM). Obviously adding
> one more is not doing it any good, but it might not make a difference in
> practice.
>
> Anyway, I agree with Julien that his suggestion is the best for ARM. If
> the libxl maintainers are willing to accept two different code paths for
> this on ARM and x86, then I am fine with it too.

Sorry to be a bit late to this thread -- there's a interface principle
that I think we should at some point have a larger discussion about:
whether "maxmem" means the amount of RAM which the guest sees as RAM,
or whether "maxmem" means the amount of RAM that the administrator
sees as used by the guest.  At the moment tnhere's no consistent
answer actually; but I am strongly of the opinion that for usability
the best answer is for "memory" to be the *total* amount of *host*
memory used by the guest.  In an ideal world, the admin should be able
to do "xl info", see that there is 3000MiB free, and then start a
guest with 3000MiB and expect it to succeed.  At the moment he has to
guess.

 -George

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