Re: [Qemu-devel] Bug with TARGET_PHYS_ADDR_SPACE_BITS

[Aurelien Jarno]

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?
> 

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 have tested support for PAE with various guests, including memtest86, 
and haven't encountered any problem.

-- 
  .''`.  Aurelien Jarno             | GPG: 1024D/F1BCDB73
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