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. Jan
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