Re: [Qemu-devel] Use of flash for x86 BIOS

[Jordan Justen]

On Sun, Apr 7, 2013 at 11:06 PM, Xiao Guangrong
<address@hidden> wrote:
> On 03/23/2013 03:09 AM, Jordan Justen wrote:
>
>> Admittedly, I've been completely ineffectual in resolving the kvm
>> portion. More recently I tried to make use of KVM_MEM_READONLY to
>> address this. I was able to get an VM exit on writes to flash, but not
>> able to get the memory region to convert to full device mode so VM
>> exits would occur on reads as well. I am once again stalled...
>
> Hi Jordan,
>
> What's memory region you want to get? I should admit that I do not
> have enough background of flash, could you please explain this
> requirement more detail?

The flash memory requires two modes.

Read/Execute mode:
* Initial state
* Writes will trap to QEMU, and may transition to Device mode based on
QEMU device emulation

Device mode:
* Region is not executable
* All reads & writes will trap to QEMU
* May transition back to Read/Execute mode based on QEMU device emulation

Using KVM_MEM_READONLY I was able to get Read/Execute mode to work,
but I was not able to get the memory region to transition to Device
mode. (I couldn't get reads to trap to QEMU.)

-Jordan