Re: [Qemu-devel] [PATCH v2 3/5] Qemu: do not mark bios readonly

[Xiao Guangrong]

On 10/31/2012 02:46 PM, Jan Kiszka wrote:

>> Please allow me to clarify it more clearly.
>>
>> The flash is ROMD device means guest can not write it, any kinds of guest 
>> write
>> access on this device can cause vmexit to kvm and return to userspace.
>>
>> We should pay more attention on it if we execute the code in ROMD since we
>> can not use ROMD as stack/page table/IDT table and all other implicitly 
>> write access.
>> Of course, if you do not use ROM as those purposes, it is okay. :)
> 
> So the problem is that there is KVM code that still blindly writes to
> guest memory and does not take the memory regions' protection flag into
> account? And we cannot mark those regions read only in the host's page
> table?

KVM has the ability to catch this kind of write access on ROMD, it is just hard 
to
emulate the implicitly memory access.