On Mon, Jul 27, 2009 at 08:10:24PM +0200, Jan Kiszka wrote: > Glauber Costa wrote: > > On Mon, Jul 27, 2009 at 12:49:06PM -0500, Anthony Liguori wrote: > >> Glauber Costa wrote: > >>> On Sun, Jul 26, 2009 at 08:59:44PM +0200, Jan Kiszka wrote: > >>> > >>>> Glauber Costa wrote: > >>>> > >>>>> The goal is to get rid of the call to kvm_init. But those things > >>>>> are subtle, and often break. So do it in a separate patch, to help > >>>>> finding potential issues in future bisections. > >>>>> > >>>> Found such an issued: This patch triggers a segfault if no kvm modules > >>>> are loaded and you start qemu without -no-kvm. Please have a look. > >>>> > >>>> Jan > >>>> > >>> ok, the culprit seems to be a > >>> > >>> if (kvm_enabled()) > >>> return; > >>> > >>> in the beginning of code_gen_alloc. > >>> > >>> It is 7f3d0cbe, by Avi, and according to changelog, suggested by anthony. > >>> I however, fail to realise the purpose of this optimization. For one thing, > >>> it totally dictates that kvm has absolutely to be enabled or disabled prior > >>> to this point. No mind changing later. Also, the real deal is to be able > >>> to compile out tcg entirely. The strategy of just disabling the code gen > >>> alloc is a minor nitpick that just papers over this. > >>> > >> I agree with you in principle but I think reverting this papers over an > >> issue. > >> > >> Why are we touching code_gen_ptr when using KVM? Can someone post the > >> full back trace? > > we're not. > > > > The issue happens exactly when the kvm modules are not loaded, then we're failing > > to initialize kvm. However, in the patch that raised this issue, I'm moving > > KVM initialization to after this code path. And in qemu-kvm.git, kvm is > > enabled-by-default. So tcg code would think kvm is enabled and skip initialization, > > while kvm code will fail to really initialize itself later. > > > > Result? Mayhem. > > > > I think we should simply resolves this the way upstream does: Do not > start if modules are missing and -no-kvm is omitted - or even switch > over to -enable-kvm as I think you already suggested in some other > thread. Then we can either fail or succeed, but not fall back more or > less silently. This falling back of qemu-kvm to tcg is a constant source > of confusion anyway. switching to --enable-kvm would be my preferred solution, but guys from mgmt tools may not like it. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
