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

Aurelien Jarno
2010-03-06T21:31:19Z

On Thu, Mar 04, 2010 at 03:34:34PM -0600, Ryan Harper wrote:
> * Aurelien Jarno <aurelien@aurel32.net> [2010-03-04 15:27]:
> > On Tue, Feb 23, 2010 at 06:02:15PM +0100, Aurelien Jarno wrote:
> > > Ryan Harper a écrit :
> > > > 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.
> > >
> > > It looks like workarounding the real bug. At some point both
> > > i386-softmmu (via PAE) and x86_64-softmmu were able to support > 4GB of
> > > memory. I remember adding the support long time ago, and testing it with
> > > 32GB of emulated RAM.
> >
> > I have looked into that, and actually one patch to get full support for
> > > 4GB of memory was not merged:
>
> Thanks for looking into this.
>
> >
> > diff --git a/exec.c b/exec.c
> > index 8389c54..b0bb058 100644
> > --- a/exec.c
> > +++ b/exec.c
> > @@ -166,7 +166,7 @@ typedef struct PhysPageDesc {
> > */
> > #define L1_BITS (TARGET_VIRT_ADDR_SPACE_BITS - L2_BITS - TARGET_PAGE_BITS)
> > #else
> > -#define L1_BITS (32 - L2_BITS - TARGET_PAGE_BITS)
> > +#define L1_BITS (TARGET_PHYS_ADDR_SPACE_BITS - L2_BITS - TARGET_PAGE_BITS)
> > #endif
> >
> > #define L1_SIZE (1 << L1_BITS)
> >
> > While this patch is acceptable for qemu i386, it creates a big L1 table
> > for x86_64 or other 64-bit architectures, resulting in huge memory
> > overhead.
> >
> > The recent multilevel tables patches from Richard Henderson should fix
> > the problem for HEAD (I haven't found time to look at them in details).
> >
> > As this is not something we really want to backport, your patch makes
> > sense in stable-0.12.
>
> Anthony, do you want me to resend and rebase against 0.12-stable?
>

The patch applies correctly on stable-0.12. I have just applied it.

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