lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Wed, 21 Dec 2011 04:26:48 +0800 From: "Liu, Jinsong" <jinsong.liu@...el.com> To: Alexey Zaytsev <alexey.zaytsev@...il.com> CC: Kernel development list <linux-kernel@...r.kernel.org>, Jan Kiszka <jan.kiszka@...mens.com>, Marcelo Tosatti <mtosatti@...hat.com>, Avi Kivity <avi@...hat.com>, Garrett D'Amore <garrett@...enta.com> Subject: RE: [Regression, bisected] a3e06bbe8445f57eb949e6474c5a9b30f24d2057: KVM: emulate lapic tsc deadline timer for guest" Alexey Zaytsev wrote: > On Tue, Dec 20, 2011 at 22:19, Liu, Jinsong <jinsong.liu@...el.com> > wrote: >> Alexey Zaytsev wrote: >>> On Tue, Dec 20, 2011 at 21:21, Liu, Jinsong <jinsong.liu@...el.com> >>> wrote: >>>> Linus Torvalds wrote: >>>>> On Tue, Dec 20, 2011 at 1:51 AM, Alexey Zaytsev >>>>> <alexey.zaytsev@...il.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. > > It does, if available. Please check > https://github.com/illumos/illumos-gate/blob/master/usr/src/uts/i86pc/io/pcplusmp/apic_timer.c#L290 > and where do you pull qemu? and commit number? I usually use Avi's qemu-kvm. Thanks, Jinsong -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists