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Re: [Xen-devel] [PATCH v2 32/41] arm : acpi dynamically map mmio regions

On Fri, Jul 31, 2015 at 4:09 PM, Stefano Stabellini
<stefano.stabellini@xxxxxxxxxxxxx> wrote:


> One option going forward is to map MMIO regions in Dom0 on demand when
> trapping in Xen with a data abort. Specifically in
> xen/arch/arm/traps.c:do_trap_data_abort_guest we could check that the
> guest is dom0 and that the address correspond to a non-ram region not
> owned by Xen. If the checks succeed then we map the page in Dom0.

I seem to remember people raising issues about mapping device memory
on-demand on KVM/arm64, because you can have weird timing issues
happening if a register map spans multiple pages etc., but i can't
seem to find the original e-mail.  I think it was Ard/Marc/Peter
discussing this.


>> >>
>> >
>> > Which boot protocol? Could you point it out? Thanks. :)
>> The way to boot DOM0 with ACPI. There is a page on the Linaro wiki [1],
>> but the content is quite out of date now.
>> Regards,
>> [1] https://wiki.linaro.org/LEG/Engineering/Virtualization/ACPI_on_Xen
> http://marc.info/?i=1431893048-5214-1-git-send-email-parth.dixit%40linaro.org
> is a good start, but it needs more details. The important thing to clear
> out is which information is passed to Dom0 and how, because it will
> become a supported external interface going forward.
> Specifically:
> - what information is passed via the small device tree to dom0 and in
>   what format
> - how the acpi tables are given to dom0
>   * mapped or copied?
>   * how do we pass a pointer to them to the kernel?
> - if some tables are changed by Xen before passing them on, it would be
>   good to list what was changed
>   * what tables have been modified
>   * what tables have been added
>   * what tables have been removed
> - how is the memory map passed to Dom0
>   * how do we find out the list of MMIO regions, both temporary and
>     future solutions
>   * how to we tell dom0 where they are

Also, is there going to be some paravirtualized interface for the info
that systems would normally get from UEFI, or are we going to emulate
UEFI, or is all this going to be in the small DT?

(I know this has been discussed before, but I have forgotten the conclusions)


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