Re: [Xen-devel] HVMlite ABI specification DRAFT B + implementation outline

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 09/02/16 14:36, Boris Ostrovsky wrote:
> On 02/09/2016 06:58 AM, Roger Pau Monnà wrote:
>> El 9/2/16 a les 11:56, Andrew Cooper ha escrit:
>>> On 08/02/16 19:03, Roger Pau Monnà wrote:
>>>>
>>>> Description of physical hardware devices will always come from
>>>> ACPI, in the
>>>> absence of any physical hardware device no ACPI tables will be
>>>> provided. The
>>>> presence of ACPI tables can be detected by finding the RSDP, just
>>>> like on
>>>> bare metal.
>>> As we are extending the base structure, why not have an RSDP paddr
>>> in it
>>> as well?  This avoids the need to scan RAM, and also serves as an
>>> indication of "No ACPI".
>> Right, this seems fine to me. I can send a patch later to expand the
>> structure unless anyone else complains.
>>
>
> Isn't scanning memory the standard procedure for finding RSDP?

For BIOS boot, yes.  For EFI, not necessarily.

> Even if we provide the address, guests will still search the memory
> (or is it just Linux that does that?)

A suitably enlightened guest need not scan memory if it is has a direct
pointer to the ACPI tables.  A guest might still scan memory, but all it
is doing is wasting time.

~Andrew

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