On 2012-10-29 08:09, Xiao Guangrong wrote: > Jan, > > On 10/26/2012 06:35 PM, Jan Kiszka wrote: > >> This has two problems: We know it breaks at least Win 95 that overwrites >> its F-segment during boot. And it applies changes to the shadowed area >> (below 1 MB) also to the ROM area - I don't think that is the original >> behaviour on real hardware. > > So what is the problem? It can break Win95's running? > > I tried to install win95 guest but it failed to boot regardless my patchset > was applied or not. I found the information that win 95 is not supported at > http://www.linux-kvm.org/page/Guest_Support_Status > > Note: before my patchset, Win 95 still can happily something into ROM area > because readonly memory is actually writable on KVM. And win95 can not run > on isapc with --no-kvm since it is no way to enable shadow ROM. Your patches causes regressions on TCG mode as that is perfectly fine with booting Win95 so far. > >> >> What we need is paravirtual shadow write control for the ISA PC. It's on >> my todo list, maybe I will be able to look into this during the next week. >> > > You idea is that modify the code of seabios and use a special way (PV) to > notify Qemu to make the bios writable? Yes. > > Actually, I am confused why the guest (including bios) persistently uses > shadow ROM even if it is not supported (on ISA PC), i think the right way > is move itself to RAM under this case, no? I've been told that Seabios has been built around that assumption and the PV shadow control would be simpler to realize. > >> BTW, your patch series should allow to drop the KVM special case from >> pc_system_firmware_init. That version, btw, treats high and low BIOS >> areas separately - but only reloads the upper area. Hmm... >> > > You mean that also allow Qemu to use pflash to load bios if kvm is enabled? Yes. > We can not do that for pflash is a RD device which can not be directly written, > kvm can not emulate the instruction which implicitly write the memory. (e.g: > using this area as stack). Isn't enabling ROMD support for KVM that whole point of your patches? I do not see yet what prevents this still, but it should be fixed first. Jan
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