qemu-devel
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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


From: Anthony Liguori
Subject: Re: [Qemu-devel] [RFC] Memory API
Date: Thu, 19 May 2011 08:44:12 -0500
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110424 Lightning/1.0b2 Thunderbird/3.1.10

On 05/19/2011 04:10 AM, Avi Kivity wrote:
On 05/19/2011 12:08 PM, Gleb Natapov wrote:
On Wed, May 18, 2011 at 06:42:14PM +0300, Avi Kivity wrote:
> On 05/18/2011 06:36 PM, Jan Kiszka wrote:
> >>
> >> We need to head for the more hardware-like approach. What happens
when
> >> you program overlapping BARs? I imagine the result is
> >> implementation-defined, but ends up with one region decoded in
> >> preference to the other. There is simply no way to reject an
> >> overlapping mapping.
> >
> >But there is also now simple way to allow them. At least not without
> >exposing control about their ordering AND allowing to hook up managing
> >code (e.g. of the PCI bridge or the chipset) that controls
registrations.
>
> What about memory_region_add_subregion(..., int priority) as I
> suggested in another message?
Haven't saw another message yet, but how caller knows about priority?

The caller is emulating some hub or router and should decide on priority
like real hardware.

For example, piix gives higher priority to the vga window over RAM.

Well......

The i440fx may direct VGA accesses to RAM depending on the SMM registers. By the time the PIIX gets the I/O request, we're past the memory controller.

This is my biggest concern about this whole notion of "priority". These sort of issues are not dealt with by a simple z-ordering. There is logic in each component that may be arbitrarily complex.

We're going to end up having to dynamically change the "priority" based how registers are programmed. But priorities are relative so it's unclear to me how the I440FX would prioritize RAM over dispatch to PIIX (for VGA, for instance).

Regards,

Anthony Liguori



reply via email to

[Prev in Thread] Current Thread [Next in Thread]