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. 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 -- 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
