Re: [Qemu-devel] [PATCH v7 1/4] isapc: Fix non-KVM qemu boot (read/write memory for isapc BIOS)

[Kevin O'Connor]

On Fri, May 31, 2013 at 02:48:17PM +0200, Paolo Bonzini wrote:
> Il 31/05/2013 04:06, Kevin O'Connor ha scritto:
> > On Wed, May 29, 2013 at 01:27:24AM -0700, Jordan Justen wrote:
> >> > The isapc machine with seabios currently requires the BIOS region
> >> > to be read/write memory rather than read-only memory.
> >> > 
> >> > KVM currently cannot support the BIOS as a ROM region, but qemu
> >> > in non-KVM mode can. Based on this, isapc machine currently only
> >> > works with KVM.
> >> > 
> >> > To work-around this isapc issue, this change avoids marking the
> >> > BIOS as readonly for isapc.
> > How about changing the code to always make the ROM read/write (instead
> > of doing it only on isapc).  Currently, if the rom is marked as
> > read-only, then SeaBIOS makes it read/write as the first thing it
> > does.  So, making it read-only doesn't really serve any purpose.
> 
> I don't think SeaBIOS can rely on the value of the PAM registers when it
> is started via a CPU reset (INIT), can it?

SeaBIOS currently detects the PAM registers at startup - if it is in
read-only mode it makes it read/write.  If it's in read/write mode it
leaves it there.  That's why I think it is silly to start in read-only
mode - the first thing the guest does is make it read/write.

-Kevin