Messages in this thread | | | From | "Liu, Jinsong" <> | Date | Wed, 21 Dec 2011 04:19:12 +0800 | Subject | RE: [Regression, bisected] a3e06bbe8445f57eb949e6474c5a9b30f24d2057: KVM: emulate lapic tsc deadline timer for guest" |
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Alexey Zaytsev wrote: > On Tue, Dec 20, 2011 at 21:21, Liu, Jinsong <jinsong.liu@intel.com> > wrote: >> Linus Torvalds wrote: >>> On Tue, Dec 20, 2011 at 1:51 AM, Alexey Zaytsev >>> <alexey.zaytsev@gmail.com> wrote: >>>> >>>> Let me clarify the situation. >>>> >>>> Before this commit, the tsc was advertised in cpuid, and it was >>>> handled, if I understand things correctly, by qemu. >>>> After this commit, the tsc is advertised in cpuid, and is handled >>>> in the kernel, but only after qemu issues KVM_CREATE_IRQCHIP. If >>>> it does not issue the ioctl, the kernel just discards any wrmsrs >>>> done to the tsc. This does not look like an Illumos problem to me. >>>> Linux guests kind of work here, because they are prepared to work >>>> on utterly broken hardware. Good for you, but please don't break >>>> less-prepared guests. >>> >>> Yes. This is a regression, and needs to be fixed. >>> >>> Liu, if you don't have time to debug it, we'll just revert the >>> commit. It's that easy. Regressions are not allowed. There are no >>> excuses. >>> >>> In particular, saying "just wait for qemu-kvm" is not an acceptable >>> answer, because the point is that things *used* to work, and they >>> broke. No "change it to work with the new kernel" allowed, except >>> for some *very* rare critical circumstances (usually "major >>> security-bug that we had to fix, and people who relied on it are >>> thus out of luck"). >>> >>> Commit a3e06bbe8445 still seems to revert cleanly, so that is the >>> easy option. >>> >>> That said, it sounds like maybe another solution is to start with >>> the TSC_DEADLINE timer bit in cpuid cleared, and only setting it >>> after the KVM_CREATE_IRQCHIP ioctl. >>> >>> In fact, the patch is clearly buggy, in that it apparently doesn't >>> emulate TSC_DEADLINE correctly and natively on its own. >>> >>> Jan, Marcelo, Avi - is there a quick fix, or should I just revert? >>> >>> And please don't *EVER* tell people that they should just work >>> around regressions. Regressions are absolutely unacceptable. Kernel >>> people need to understand that. >>> >>> Linus >> >> Yes, my fault to say 'walk around' before knowing Alex's issue >> clearly. >> >> After Alex send his last email to clarify the situation, I have >> checked the bug. >> Basically it caused from >> 1. qemu didn't issue KVM_CREATE_IRQCHIP, hence >> irqchip_in_kernel(kvm) fail when setup vcpu lapic logic at >> kvm_arch_vcpu_init(); >> 2. tsc deadline work based on vcpu lapic, hence break illumos; >> >> A fix is to update cpuid, as you said, setting it after >> KVM_CREATE_IRQCHIP. I just wonder is there any better solution? so I >> ask Alex his environment to setup at my side to do more test. If you >> think kvm tsc deadline timer patch itself not clean, please tell me. > > [Removed Linus from CC] > > If your internet connection is good enough, I could just pass you the > disk image. It should be around 5g when compressed. Otherwise, you can > download an openindiana disk image from http://openindiana.org. You > probably want the text-only "server" one. The TSC code has changed > since that release, but the old one does not work as well.
I mean I will build environment at my side with your qemu version (where do you pull from? commit number?) --> just to verify whether we can solve it at qemu side, or, solve it by cpuid at kvm side. I will present a patch to fix it and you can test at your environment.
> > Do I get it right that Linux does not use the tsc deadline timer? I've > added printks to the > kvm_get_lapic_tscdeadline_msr/kvm_set_lapic_tscdeadline_msr functions, > and I swear I've seen them trigger a few times with the Linux guest. > But I can't find the code that is issuing the msr reads/writes in the > Linux kernel.
I will check it tomorrow, too late now. and would you please tell me, does illumos use tsc deadline timer? I lack this basic information.
Thanks, Jinsong-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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