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Re: [Qemu-devel] [PATCH] Fix segfault with ram_size > 4095M without kvm
From: |
Ryan Harper |
Subject: |
Re: [Qemu-devel] [PATCH] Fix segfault with ram_size > 4095M without kvm |
Date: |
Thu, 4 Mar 2010 15:34:34 -0600 |
User-agent: |
Mutt/1.5.6+20040907i |
* Aurelien Jarno <address@hidden> [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?
--
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
address@hidden