On Tue, Nov 03, 2009 at 11:01:00PM +0900, Isaku Yamahata wrote: > On Tue, Nov 03, 2009 at 02:39:06PM +0200, Michael S. Tsirkin wrote: > > On Tue, Nov 03, 2009 at 02:22:07PM +0200, Avi Kivity wrote: > > > On 11/03/2009 01:47 PM, Michael S. Tsirkin wrote: > > >> > > >> If qemu is compiled with target phys address size 32 bit, emulated > > >> devices can not support a 64 bit BAR. Therefore, according to PCI spec, > > >> such devices should declare all BARs as 32 bit. > > Here is the point. > > "emulated devices can not support a 64 bit BAR" > If target_phy_addr_t = uint32_t, the emulation of 64 bit BAR which > is set to >4GB is cpu can't access it. So just not-mapping it > is correct behavior. > > > > > What happens if you take a PCI card that supports 64-bit BARs and stick > > > it into a machine that has a 32-bit physical address space? > > > The firmware/OS will configure the BARs to below 4G. > > > > > >> I think you are right that guests on such systems really do not have a > > >> way to address PCI devices if BAR is set beyond 4G. But pci emulation is > > >> better off not relying on this, IMO. Makes sense? > > >> > > > > > > No. Device emulation shouldn't change with the machine type. > > > > I agree. Issue is, we recompile the *devices* as well. > > It's the device emulation that is broken when compiled > > with target phys addr set to 32 bit, because all devices > > take pcibus_t and cast it to target_phys_addr_t > > and then do stuff with it. > > So such emulation should not claim to support 64 bit. > > Such case is checked by "last_addr >= TARGET_PHYS_ADDR_MAX", > so the device emulation works well. > > Generally device drivers know their devices. For example they know > that BAR0 is 64bit memory and so on. So if BAR type were changed > by forcing 64 bit BAR into 32 bit BAR, the device driver wouldn't be > confused. > > > Long term, we should fix all devices and *then* they can claim 64 bit > > support always. As a nice side effect, we'll be able to avoid > > rebuilding devices. > > Are you claiming that (PCI) devices emulation shouldn't depend on > target_phys_addr_t? That sounds a good idea.
Yes. Maybe we can stop devices from mapping memory, have pci core do it for them. > However I don't agree on "*then*". > The conversions would take place step by step as it's long term object. > I don't see any reason to penalize correct device emulations just > because there are incomplete device emulations left. Hmm. Okay ... but which device emulations are correct? It seems that none of them are. I don't see the rush . > thanks, > -- > yamahata
