On Sat, Mar 03, 2012 at 10:56:02PM -0800, Jordan Justen wrote: > On Tue, Oct 25, 2011 at 00:47, Avi Kivity <avi@xxxxxxxxxx> 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. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
