On 08/04/2010 08:34 AM, Gleb Natapov wrote:
On Wed, Aug 04, 2010 at 08:15:04AM -0500, Anthony Liguori wrote:
On 08/04/2010 08:07 AM, Gleb Natapov wrote:
On Wed, Aug 04, 2010 at 08:04:09AM -0500, Anthony Liguori wrote:
On 08/04/2010 03:17 AM, Avi Kivity wrote:
For playing games, there are three options:
- existing fwcfg
- fwcfg+dma
- put roms in 4GB-2MB (or whatever we decide the flash size is)
and have the BIOS copy them
Existing fwcfg is the least amount of work and probably
satisfactory for isapc. fwcfg+dma is IMO going off a tangent.
High memory flash is the most hardware-like solution, pretty easy
>from a qemu point of view but requires more work.
The only trouble I see is that high memory isn't always available.
If it's a 32-bit PC and you've exhausted RAM space, then you're only
left with the PCI hole and it's not clear to me if you can really
pull out 100mb of space there as an option ROM without breaking
something.
We can map it on demand. Guest tells qemu to map rom "A" to address X by
writing into some io port. Guest copies rom. Guest tells qemu to unmap
it. Better then DMA interface IMHO.
That's what I thought too, but in a 32-bit guest using ~3.5GB of
RAM, where can you safely get 100MB of memory to full map the ROM?
If you're going to map chunks at a time, you are basically doing
DMA.
This is not like DMA event if done in chunks and chunks can be pretty
big. The code that dials with copying may temporary unmap some pci
devices to have more space there.
That's a bit complicated because SeaBIOS is managing the PCI devices
whereas the kernel code is running as an option rom. I don't know the
BIOS PCI interfaces well so I don't know how doable this is.
Maybe we're just being too fancy here.
We could rewrite -kernel/-append/-initrd to just generate a floppy image
in RAM, and just boot from floppy.
Regards,
Anthony Liguori
And what's the upper limit on ROM size that we impose? 100MB is
already at the ridiculously large size.
Agree. We have two solutions:
1. Avoid the problem
2. Fix the problem.
Both are fine with me and I prefer 1, but if we are going with 2 I
prefer something sane.
--
Gleb.
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