Re: [Qemu-devel] [RFC] Memory API

[Jan Kiszka]

On 2011-05-19 10:13, Avi Kivity wrote:
> On 05/19/2011 11:08 AM, Jan Kiszka wrote:
>> On 2011-05-19 10:06, Avi Kivity wrote:
>> >  On 05/18/2011 10:40 PM, Jan Kiszka wrote:
>> >>  On 2011-05-18 15:12, Avi Kivity wrote:
>> >>  >   void cpu_register_memory_region(MemoryRegion *mr,
>> >>  target_phys_addr_t addr);
>> >>
>> >>  OK, let's allow overlapping, but make it explicit:
>> >>
>> >>  void cpu_register_memory_region_overlap(MemoryRegion *mr,
>> >>                                           target_phys_addr_t addr,
>> >>                                           int priority);
>> >>
>> >>  We need that ordering, so we need an interface. Regions registered
>> via
>> >>  cpu_register_memory_region must not overlap with existing one or
>> we will
>> >>  throw an hwerror. And they shall get a low default priority.
>> >>
>> >
>> >  PCI BARs can overlap with anything.  So any region can overlap with
>> any
>> >  other region.
>>
>> I know, but that result is unspecified anyway. The user (guest OS) can't
>> expect any reasonable result. We rather need priorities for useful
>> overlapping.
> 
> Unspecified doesn't mean abort.  It means we need to specify something
> (which translates to: we get to pick the priorities).

Of course, PCI bars would have to be registered via
cpu_register_memory_region_overlap, just specifying the default
priority. Here we know that overlapping can happen and is not a bug in
the board emulation. I want to avoid that such use cases make
overlapping generally legal, papering over real bugs.

Jan

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