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

[Gleb Natapov <gleb@redhat.com>]

On Mon, Apr 08, 2013 at 01:18:10AM -0700, Jordan Justen wrote:
> On Sun, Apr 7, 2013 at 11:06 PM, Xiao Guangrong
> <xiaoguangrong@linux.vnet.ibm.com> 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.)
> 
You need to drop memslot when you transition to Device mode.

--
			Gleb.