Re: [Qemu-devel] [PATCH] exec: fix regression by making system-memory region UINT64_MAX size

[Peter Maydell]

On 7 November 2013 21:38, Marcel Apfelbaum <address@hidden> wrote:
> Thanks Paolo,
> Let me just point out what I know (or I think I know):
> 1. Not all architectures have the behavior: "Address space that is not 
> RAM(and friends) is for sure PCI".
>    Only x86 behaves like this (I think).

More specifically, the x86 pc behaves like this. Other
x86 based systems could in theory behave differently
(not that we actually model any, I think).

> That means that you cannot have a 64bit wide pci-hole
>    with lower priority that catches all accesses that are not for RAM(and 
> firends).

...but this conclusion is wrong, because the pci-hole
region is created by the pc model. So we should create
it at the correct priority and size to give the behaviour
relative to other devices in the pc model that is required
(ie that the hardware has). This doesn't affect any other
target architecture or board.

That said, I don't know enough about the PC to know what
the exact details of the pci-hole are, so I'm not making a
statement about what the correct model is. I'm just saying
that what you do with the pci-hole and the container it lives
in and the other devices in that container is not going to
change the behaviour of any other target board.

> 2. If the above is right, and making pci-hole 64 bit wide is not an option,
>    playing with pci-holes/other-region priorities it would be just wrong,
>    it would be only to "fight" with the locality of the memory region's 
> priority.

I have no idea what you mean by "fighting" here. MR priorities
apply only within a specific container region[*], to set which of
that container's children appears 'above' another. They're
totally local to the container (which in this case is part of the
PC model, not the generic PCI code) and so the PC model
can freely set them to whatever makes most sense.

[*] if you didn't already know this, see the recently committed
updates to doc/memory.txt for a more detailed explanation.

-- PMM