[Qemu-devel] Re: [PATCH] Fix segfault with ram_size > 4095M without kvm

[Aurelien Jarno <aurelien@aurel32.net>]

On Wed, Dec 08, 2010 at 04:27:45PM -0200, Luiz Capitulino wrote:
> On Wed, 08 Dec 2010 12:23:12 -0600
> Anthony Liguori <aliguori@linux.vnet.ibm.com> wrote:
> 
> > On 12/08/2010 12:01 PM, Luiz Capitulino wrote:
> > > Currently, x86_64-softmmu qemu segfaults when trying to use>  4095M memsize.
> > > This patch adds a simple check and error message (much like the 2047 limit on
> > > 32-bit hosts) on ram_size in the control path after we determine we're
> > > not using kvm
> > >
> > > Upstream qemu-kvm is affected if using the -no-kvm option; this patch address
> > > the segfault there as well.
> > >
> > > Signed-off-by: Ryan Harper<ryanh@us.ibm.com>
> > > Signed-off-by: Aurelien Jarno<aurelien@aurel32.net>
> > > ---
> > > NOTE: this patch was applied in the v0.12.x branch, but it seems it got
> > >        lost for master
> > >    
> > 
> > No, it was intentional.  We should fix the segv, this is not a known 
> > limitation but rather a bug.
> 
> A TCG bug, I presume?
> 

Do you have more details about this issue and how to reproduce it? 

Support for more than 4GB of memory has been added a few years ago, 
and I am not able to reproduce the problem anymore (I have booted a 
64-bit guest with 6GB of RAM, and make sure the guest use the whole 
memory). I guess TCG itself is fine, but there might be a bug in
the MMU emulation in some cases.

I also noticed that now i386-softmmu has been artificially limited to
2047MB. Tthis configuration used to support up to 64GB of RAM (PAE)
on 64-bit hosts.

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel33.net