Re: [Qemu-devel] [PATCH 13/27] acpi: memory hotplug ACPI hardware implementation

[Paolo Bonzini]

Il 25/11/2013 15:18, Igor Mammedov ha scritto:
>> > For example on reset all slots could be disabled by the
>> > ACPIHotpluggableDimmBus (even coldplugged ones), and scanned + enabled
>> > by ASL.
> memory devices are scanned by OSPM during ACPI tables parsing and 
> guest (can) use present devices right away.

Yes, what I'm saying is scan them to enable them so that OSPM sees them
already as online.

> Currently I don't see necessity for enabling individual memory devices from
> ASL since it adds one more round trip for QEMU<->guest protocol for no
> particular benefit. The only use case Michael suggested would be running
> OLD BIOS (without memory hotplug support) on machine with actively used
> memory hotplug (if OLD BIOS runs on machine with memory hotplug but there is
> no hotplugged memory devices, it runs just fine), so case looks like not worth
     ^^^^^^^^^^

*Hotpluggable*, not hotplugged.  It would also break just with
coldplugged memory devices.

> That would allow later to put present at boot DIMMs into E820 (way before ASL
> is executed) if that would be necessary and also help to convert initial
> memory into hotpluggable one as well.

I am afraid that mixing hot-unplug with E820 could cause some
unanticipated trouble.  OSes may not expect memory in the E820 ranges to
disappear.

But since we're speaking about e820, do guests work if you make the
hotpluggable memory region reserved in the e820?  That should work with
old BIOS too using QEMU_CFG_E820_TABLE.  If that works, I see no need
for an "enabled" bit either.

Paolo

> an effort and complexity it would bring.