On Mon, Sep 24, 2012 at 3:44 PM, Avi Kivity <a...@redhat.com> wrote: > On 09/24/2012 08:33 AM, liu ping fan wrote: >> On Wed, Sep 19, 2012 at 5:50 PM, Avi Kivity <a...@redhat.com> wrote: >> > On 09/19/2012 12:34 PM, Jan Kiszka wrote: >> >> >> >> What about the following: >> >> >> >> What we really need to support in practice is MMIO access triggers RAM >> >> access of device model. Scenarios where a device access triggers another >> >> MMIO access could likely just be rejected without causing troubles. >> >> >> >> So, when we dispatch a request to a device, we mark that the current >> >> thread is in a MMIO dispatch and reject any follow-up c_p_m_rw that does >> >> _not_ target RAM, ie. is another, nested MMIO request - independent of >> >> its destination. How much of the known issues would this solve? And what >> >> would remain open? >> > >> > Various iommu-like devices re-dispatch I/O, like changing endianness or >> > bitband. I don't know whether it targets I/O rather than RAM. >> > >> Have not found the exact code. But I think the call chain may look >> like this: dev mmio-handler --> c_p_m_rw() --> iommu mmio-handler --> >> c_p_m_rw() >> And I think you worry about the case for "c_p_m_rw() --> iommu >> mmio-handler". Right? How about introduce an member can_nest for >> MemoryRegionOps of iommu's mr? >> > > I would rather push the iommu logic into the memory API: > > memory_region_init_iommu(MemoryRegion *mr, const char *name, > MemoryRegion *target, MemoryRegionIOMMUOps *ops, > unsigned size) > > struct MemoryRegionIOMMUOps { > target_physical_addr_t (*translate)(target_physical_addr_t addr, > bool write); > void (*fault)(target_physical_addr_t addr); > }; > So I guess, after introduce this, the code logic in c_p_m_rw() will look like this
c_p_m_rw(dev_virt_addr, ...) { mr = phys_page_lookup(); if (mr->iommu_ops) real_addr = translate(dev_virt_addr,..); ptr = qemu_get_ram_ptr(real_addr); memcpy(buf, ptr, sz); } > I'll look at a proposal for this. It's a generalized case of > memory_region_init_alias(). > > -- > I have a truly marvellous patch that fixes the bug which this > signature is too narrow to contain. >