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Re: [Qemu-devel] [PATCH v2 3/5] Qemu: do not mark bios readonly
From: |
Xiao Guangrong |
Subject: |
Re: [Qemu-devel] [PATCH v2 3/5] Qemu: do not mark bios readonly |
Date: |
Mon, 29 Oct 2012 15:09:12 +0800 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120911 Thunderbird/15.0.1 |
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.
>
> 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?
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?
> 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?
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).
Thanks!
- [Qemu-devel] [PATCH v2 0/5] Qemu: implement readonly memory, Xiao Guangrong, 2012/10/25
- [Qemu-devel] [PATCH v2 1/5] KVM: define KVM_CAP_READONLY_MEM unconditionally, Xiao Guangrong, 2012/10/25
- [Qemu-devel] [PATCH v2 4/5] Qemu: implement readonly memory, Xiao Guangrong, 2012/10/25
- [Qemu-devel] [PATCH v2 3/5] Qemu: do not mark bios readonly, Xiao Guangrong, 2012/10/25
- Re: [Qemu-devel] [PATCH v2 3/5] Qemu: do not mark bios readonly, Jan Kiszka, 2012/10/26
- Re: [Qemu-devel] [PATCH v2 3/5] Qemu: do not mark bios readonly,
Xiao Guangrong <=
- Re: [Qemu-devel] [PATCH v2 3/5] Qemu: do not mark bios readonly, Jan Kiszka, 2012/10/29
- Re: [Qemu-devel] [PATCH v2 3/5] Qemu: do not mark bios readonly, Xiao Guangrong, 2012/10/29
- Re: [Qemu-devel] [PATCH v2 3/5] Qemu: do not mark bios readonly, Jan Kiszka, 2012/10/31
- Re: [Qemu-devel] [PATCH v2 3/5] Qemu: do not mark bios readonly, Xiao Guangrong, 2012/10/31
- Re: [Qemu-devel] [PATCH v2 3/5] Qemu: do not mark bios readonly, Jan Kiszka, 2012/10/31
- Re: [Qemu-devel] [PATCH v2 3/5] Qemu: do not mark bios readonly, Xiao Guangrong, 2012/10/31
- Re: [Qemu-devel] [PATCH v2 3/5] Qemu: do not mark bios readonly, Jan Kiszka, 2012/10/31
[Qemu-devel] [PATCH v2 5/5] Qemu: mark pci rom readonly, Xiao Guangrong, 2012/10/25
[Qemu-devel] [PATCH v2 2/5] Qemu: update header files, Xiao Guangrong, 2012/10/25