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Re: [Qemu-devel] PC machine types switched to SeaBIOS/gPXE

From: Avi Kivity
Subject: Re: [Qemu-devel] PC machine types switched to SeaBIOS/gPXE
Date: Tue, 03 Nov 2009 07:01:52 +0200
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20090922 Fedora/3.0-3.9.b4.fc12 Thunderbird/3.0b4

On 11/03/2009 06:57 AM, Alexander Graf wrote:
Yes, I'd prefer to see this.  In earlier emails, Gleb made a reference
to a qemu-cfg "stream" interface that is used for acpi tables - maybe
the kernel could be put in one of the streams and the rom could copy
it into ram on boot.

I don't think streaming is the right approach here. Streaming would mean the rom had to copy, which again either a lot of PIO accesses (slow!) or a complicated DMA interface.

A rep/ins instruction will take one exit/page so it won't be particularly slow.

I'd rather go for a RAM poking approach. As soon as the option rom is loaded, it calls qemu via PIO telling it to "load the kernel in RAM now" and as of the next instruction everything's in place at the determined addresses. It's not like we could do anything about the physical layout in the option rom anyways, usually the kernel tells us what that looks like.

That works too, but if firmware config can use rep/ins, that's one less interface we have to add.

Do not meddle in the internals of kernels, for they are subtle and quick to 

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