Re: 2 CPU Conformance Issue in KVM/x86

Avi Kivity
2015-03-09T19:49:23Z

On 03/09/2015 09:38 PM, Paolo Bonzini wrote:
>
> On 09/03/2015 20:19, Avi Kivity wrote:
>> I can't think of one with reasonable performance either. Perhaps the
>> maintainers could raise the issue with Intel. It looks academic but it
>> can happen in real life -- KVM for example used to rely on reserved bits
>> faults (it set all bits in the PTE so it wouldn't have been caught by
>> this).
> Yes, and it checked that MAXPHYADDR != 52 before. If you want to set
> only one bit, making that bit 51 makes sense anyway for simplicity, so
> it is still 99.9% academic. Once processors appear with MAXPHYADDR =
> 52, the remaining 0.1% will become more relevant.
>
> The current limit is IIRC 46 or 48 (on Haswell Xeons).
>

It will be interesting to have processors with 52 bits of physical
address and 48 bits of virtual address. HIGHMEM for x86_64? Or 5-level
page tables?

50 bits == 1 PiB. That's quite an amount of RAM.