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Re: [Qemu-devel] Re: [PATCH V6 17/32] pci: 64bit bar support.


From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] Re: [PATCH V6 17/32] pci: 64bit bar support.
Date: Tue, 3 Nov 2009 14:39:06 +0200
User-agent: Mutt/1.5.19 (2009-01-05)

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.
>>
>>    
>
> 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.

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.

> -- 
> error compiling committee.c: too many arguments to function




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