Re: [Qemu-devel] KVM/QEMU: Support executing from flash device

[Avi Kivity]

On 03/04/2012 12:38 PM, Gleb Natapov wrote:
> On Sun, Mar 04, 2012 at 12:36:20PM +0200, Avi Kivity wrote:
> > On 03/04/2012 10:12 AM, Gleb Natapov wrote:
> > > On Sat, Mar 03, 2012 at 10:56:02PM -0800, Jordan Justen wrote:
> > > > On Tue, Oct 25, 2011 at 00:47, Avi Kivity <address@hidden> wrote:
> > > > > The core issue that kvm (the kernel part) supports two styles of 
> > > > > memory:
> > > > > read/write RAM, and read/write MMIO.  ROM wants writes to be ignored,
> > > > > and rom/device wants reads serviced from memory and writes serviced by
> > > > > userspace (as MMIO).
> > > > >
> > > > > It should not be too hard to patch kvm to support these additional two
> > > > > styles.  The entry point is the KVM_SET_USER_MEMORY_REGION ioctl to
> > > > > define the new attributes for the region, and kvm_mmu_page_fault() to
> > > > > map these pages as read-only and emulate writes (for ROM/device 
> > > > > regions).
> > > > 
> > > > Additional context for CC'd kvm-devel: I would like to support
> > > > executing from an emulated flash memory on kvm.  The flash memory
> > > > would be a CFI (Firmware Hub-like) device which is programmed via MMIO
> > > > at the same addresses in memory where the execution would occur.
> > > > 
> > > > What is needed is:
> > > > 1. The ability to set a region to allow read/exec,
> > > >    but trap to qemu on writes.
> > > > 2. qemu should then be able to set the region
> > > >    to trap on reads/exec/writes.
> > > Do you want to execute code from a flash while it traps on read/exec?
> > > KVM emulator can't do that.
> > 
> > No, he wants read/exec to go to RAM, and writes to be handled as mmio. 
> > This should work.
> > 
> That's mode 1 from above and will obviously work. I am asking about mode
> 2 from above.
>

Mode 2 is pure mmio.  You're right that kvm won't run code from that.

Jordan, what's the use for mode 2?  Is it just used during programming?

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