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

[Jan Kiszka]

On 2012-10-31 08:01, Xiao Guangrong wrote:
> 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.

Drop them? It is highly unlikely that they trigger the magic
write-enable patterns at the right spot in a ROMD device.

Jan

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