On Tue, May 05, 2009 at 07:49:10AM -0300, Marcelo Tosatti wrote: > 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. You could also move the emulated MSI-X table, sticking it on top of the existing BAR. Since PCI config includes the pointer to the table, a driver that reads this pointer will continue to work. Of course, there's no guarantee that guest drivers don't just hard-code this offset. > BTW this is why you can't map the MSI-X table page directly, you want > accesses to be trapped. BTW current design won't work if the base page size is > 4K, will it? The hole covers a page, so you'll get faults outside the MSI-X table. -- MST -- 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
