Re: [Xen-devel] [PATCH v3 16/17] SUPPORT.md: Add limits RFC

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 11/23/2017 11:21 AM, Jan Beulich wrote:
>>>> On 22.11.17 at 20:20, <george.dunlap@xxxxxxxxxx> wrote:
>> +### Virtual RAM
>> +
>> +    Limit-security, x86 PV 64-bit: 2047GiB
>> +    Limit-security, x86 PV 32-bit: 168GiB (see below)
>> +    Limit-security, x86 HVM: 1.5TiB
>> +    Limit, ARM32: 16GiB
>> +    Limit, ARM64: 1TiB
>> +
>> +Note that there are no theoretical limits to 64-bit PV or HVM guest sizes
>> +other than those determined by the processor architecture.
>> +
>> +All 32-bit PV guest memory must be under 168GiB;
>> +this means the total memory for all 32-bit PV guests cannot exced 168GiB.
> 
> While certainly harder to grok for the reader, I think we need to be
> precise here: The factor isn't the amount of memory, but the
> addresses at which it surfaces. Host memory must not extend
> beyond the 168MiB boundary for that to also be the limit for
> 32-bit PV guests.

Yes, I'd intended "under 168GiB" to more clearly imply physical
addresses; but I agree as written that's unlikely to be picked up by
anyone not already familiar with the concept.

What about something like this:

"32-bit PV guests can only access physical addresses below 168GiB;
this means that the total memory of all 32-bit PV guests cannot exceed
168GiB.  For hosts with more than 168GiB RAM, this limit becomes 128GiB."

 -George

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel