Re: [Qemu-devel] [PULL 14/28] exec: make address spaces 64-bit wide

[Mike Day]

On Tue, Jan 14, 2014 at 9:05 AM, Michael S. Tsirkin <address@hidden> wrote:
> On Tue, Jan 14, 2014 at 08:50:54AM -0500, Mike Day wrote:

>>
>> Also, both 32-bit and 64-bit BARs are required to be supported. It is
>> legal to construct a 64-bit BAR by masking all the high bits to
>> zero. Presumably it would be OK to mask the 16 high bits to zero as
>> well, constructing a 48-bit address.

> The question was whether addresses such as
> 0xfffffffffec00000 can be a valid BAR value on these
> platforms, whether it's accessible to the CPU and
> to other PCI devices.

The answer has to be no at least for Linux. Linux uses the high bit of
the page table address as state to indicate a huge page and uses
48-bit addresses. Each PCI device is different but right now Power7
supports 16TB of RAM so I don't think the PCI bridge would necessarily
decode the high 16 bits of the memory address. For two PCI devices to
communicate with each other using 64-bit addresses they both need to
support 64-bit memory in the same address range, which is possible.
All this info subject to Paul Mackerras or Alexy …

Mike