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Re: [Qemu-devel] KVM/QEMU: Support executing from flash device
From: |
Gleb Natapov |
Subject: |
Re: [Qemu-devel] KVM/QEMU: Support executing from flash device |
Date: |
Sun, 4 Mar 2012 10:12:34 +0200 |
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.
> 3. qemu should be able to then restore the region
> to the initial state.
>
> Here is my plan:
> 1. Add KVM_CAP_REGION_WRITE_TRAP
> 2. Add kvm_memory_region::flags
> KVM_MEMSLOT_TRAP_WRITES
> 3. Update page table creation to trap on writes when
> KVM_MEMSLOT_TRAP_WRITES is set
>
> Is this plan heading in the right direction?
>
> Regarding emulating ROM (as you mentioned above): I think that it can
> trap to qemu and QEMU can ignore it. This would be a performance hit,
> but I don't think it is expected that lots of writes to a ROM will
> occur. Do you agree?
>
> -Jordan
--
Gleb.
Re: [Qemu-devel] KVM/QEMU: Support executing from flash device, Avi Kivity, 2012/03/04