On Tue, May 05, 2009 at 01:34:50PM +0300, Michael S. Tsirkin wrote: > On Tue, May 05, 2009 at 07:19:45AM -0300, Marcelo Tosatti wrote: > > On Tue, May 05, 2009 at 12:51:36PM +0300, Michael S. Tsirkin wrote: > > > On Mon, Apr 27, 2009 at 10:30:17PM +0800, Sheng Yang wrote: > > > > > > > > If guest can write to the real device MSI-X table directly, it would > > > > > > > > cause chaos on interrupt delivery, for what guest see is totally > > > > > > > > different with what's host see... > > > > > > > > > > > > > > Obviously. > > > > > > > > > > > > > > Thanks, > > > > > > > > > > What's the reason that this page is unmapped from the qemu memory space? > > > Specifically what do these lines do: > > > int offset = r_dev->msix_table_addr - real_region->base_addr; > > > ret = munmap(region->u.r_virtbase + offset, TARGET_PAGE_SIZE); > > > > I believe this allows accesses to this page (the MSI-X table), which > > is part of the guest address space (through kvm memory slots), to be > > trapped by qemu. > > > > Since there is no actual page in this guest address, KVM treats accesses > > as MMIO and forwards them to QEMU. > > > > > > I thought about this too. > But why is this necessary for assigned MSI-X but not for emulated devices such as > e.g. e1000? All e1000 does seems to be cpu_register_physical_memory ... Because there is no registered (kvm) memory slot for the range which e1000 registers its MMIO? Not sure about the address of the MSI-X table page, but you could achieve the same effect by splitting the slot which it lives in two, with a 1 page hole between them. BTW this is why you can't map the MSI-X table page directly, you want accesses to be trapped. -- 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
