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Re: [Qemu-devel] [RFC v3 06/15] hw/arm/virt: Allocate device_memory

From: Auger Eric
Subject: Re: [Qemu-devel] [RFC v3 06/15] hw/arm/virt: Allocate device_memory
Date: Wed, 8 Aug 2018 11:33:23 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0

Hi Igor,

On 07/18/2018 03:00 PM, Igor Mammedov wrote:
>>> I think Igor wants one contiguous region for RAM, where additional
>>> space can be reserved for hotplugging.  
>> This is not compliant with 2012 ARM white paper, although I don't really
>> know if this document truly is a reference (did not get any reply).
> it's upto QEMU to pick layout, if we have maxmem (upto 256Gb) we could
> accommodate legacy req and put single device_memory in 1Gb-256Gb GPA gap,
> if it's more we can move whole device_memory to 2Tb, 8Tb ...
> that keeps things manageable for us and fits specs (if such exist).
> WE should make selection of the next RAM base deterministic is possible
> when layout changes due to maxram size or IOVA, so that we won't need
> to use compat knobs/checks to keep machine migratable.
Sorry for the delay. I was out of the office those past weeks.

OK understood. Your preferred approach is to have a contiguous memory
region (initial + hotplug). So this depends on the FW capability to
support flexible RAM base. Let's see how this dependency gets resolved.

This series does not bump the non hotpluggable memory region limit,
which is still limited to 255GB. The only way to add more memory is
though PCDIMM or NVDIMM (max 2TB atm). To do so you need to add ,maxmem
and ,slots options which need to be on both source and dest, right, +
the PCDIMM/NVDIMM device option lines? Also the series checks the
destination has at least the same IPA range capability as the source,
which conditions the fact the requested device_memory size can be
accommodated. At the moment I fail to see what are the other compat
knobs I must be prepared to handle.


> [...]

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