Messages in this thread | | | From | Andy Lutomirski <> | Date | Thu, 20 Aug 2020 08:55:22 -0700 | Subject | Re: FSGSBASE causing panic on 5.9-rc1 |
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On Thu, Aug 20, 2020 at 8:21 AM Tom Lendacky <thomas.lendacky@amd.com> wrote: > > On 8/20/20 10:10 AM, Sean Christopherson wrote: > > On Wed, Aug 19, 2020 at 05:21:33PM -0700, Andy Lutomirski wrote: > >> On Wed, Aug 19, 2020 at 2:25 PM Andy Lutomirski <luto@kernel.org> wrote: > >>> > >>> On Wed, Aug 19, 2020 at 11:19 AM Tom Lendacky <thomas.lendacky@amd.com> wrote: > >>>> > >>>> On 8/19/20 1:07 PM, Tom Lendacky wrote: > >>>>> It looks like the FSGSBASE support is crashing my second generation EPYC > >>>>> system. I was able to bisect it to: > >>>>> > >>>>> b745cfba44c1 ("x86/cpu: Enable FSGSBASE on 64bit by default and add a chicken bit") > >>>>> > >>>>> The panic only happens when using KVM. Doing kernel builds or stress > >>>>> on bare-metal appears fine. But if I fire up, in this case, a 64-vCPU > >>>>> guest and do a kernel build within the guest, I get the following: > >>>> > >>>> I should clarify that this panic is on the bare-metal system, not in the > >>>> guest. And that specifying nofsgsbase on the bare-metal command line fixes > >>>> the issue. > >>> > >>> I certainly see some oddities: > >>> > >>> We have this code: > >>> > >>> static void svm_vcpu_put(struct kvm_vcpu *vcpu) > >>> { > >>> struct vcpu_svm *svm = to_svm(vcpu); > >>> int i; > >>> > >>> avic_vcpu_put(vcpu); > >>> > >>> ++vcpu->stat.host_state_reload; > >>> kvm_load_ldt(svm->host.ldt); > >>> #ifdef CONFIG_X86_64 > >>> loadsegment(fs, svm->host.fs); > >>> wrmsrl(MSR_KERNEL_GS_BASE, current->thread.gsbase); > > > > Pretty sure current->thread.gsbase can be stale, i.e. this needs: > > > > current_save_fsgs(); > > I did try adding current_save_fsgs() in svm_vcpu_load(), saving the > current->thread.gsbase value to a new variable in the svm struct. I then > used that variable in the wrmsrl below, but it still crashed.
Can you try bisecting all the way back to:
commit dd649bd0b3aa012740059b1ba31ecad28a408f7f Author: Andy Lutomirski <luto@kernel.org> Date: Thu May 28 16:13:48 2020 -0400
x86/cpu: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE
and adding the unsafe_fsgsbase command line option while you bisect.
Also, you're crashing when you run a guest, right? Can you try running the x86 sefltests on a bad kernel without running any guests?
--Andy
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