Re: [Qemu-devel] Bug with TARGET_PHYS_ADDR_SPACE_BITS

[Anthony Liguori <anthony@codemonkey.ws>]

Chris Lalancette wrote:
> Aurelien Jarno wrote:
>   
>> On Tue, Aug 19, 2008 at 07:46:50PM +0200, Chris Lalancette wrote:
>>     
>>> Hello,
>>>      oVirt is currently using straight x86_64 qemu emulation for certain parts
>>> of the architecture (we mostly use KVM, but need to use full emulation for a
>>> couple of parts).  We recently upgraded our userspace package to kvm-72, but
>>> found that we could not PXE boot guests when we were doing full emulation (under
>>> kvm, we could PXE boot just fine).  We also tried using qemu SVN tip, with
>>> similar results.  We ended up doing a bisect, and tracked down the problem to
>>> this commit (from the kvm repo, but pulled from qemu):
>>>
>>> http://git.kernel.org/?p=linux/kernel/git/amit/kvm-userspace.git;a=commit;h=468f7507339a5236bff8ab339eb0c1b019a95fda
>>>
>>> The important changes in there in terms of this bug revolves around
>>> TARGET_PHYS_ADDR_SPACE_BITS in exec.c.  If I change that back to 32 (what it was
>>> before this patch for x86_64), the PXE boot succeeds.  Also, if I remove
>>> TARGET_PHYS_ADDR_SPACE_BITS > 32 conditional code in phys_page_find_alloc(), but
>>> leave TARGET_PHYS_ADDR_SPACE_BITS as 42, the PXE boot also works.  I can't claim
>>> to understand the conditional code I've compiled out, so I'm not sure where the
>>> bug would be.  Does anyone have an idea what the problem might be?
>>>
>>>       
>
> Sorry for the delay in responding.
>
>   
>> Are you using qemu or qemu-system-x86_64? Could you also build qemu with
>> --disable-kqemu? It possible that kqemu support is causing this problem,
>> as it is limited to 32 bits.
>>     
>
> I'm not sure what the difference between qemu and qemu-system-x86_64 is.  Can
> you explain?  I've been testing with qemu-system-x86_64, for what it's worth.
>   

qemu is really qemu-system-i386 just unfortunately named.  This define 
will differ in the qemu vs qemu-system-x86_64 binaries.

Has there been any resolution here?

Regards,

Anthony Liguori