[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 1/2] VMX: fix VMCS race on context-switch paths
>>> On 15.02.17 at 12:55, <JBeulich@xxxxxxxx> wrote: >>>> On 15.02.17 at 12:48, <sergey.dyasli@xxxxxxxxxx> wrote: >> On Wed, 2017-02-15 at 04:39 -0700, Jan Beulich wrote: >>> > > > On 15.02.17 at 11:27, <sergey.dyasli@xxxxxxxxxx> wrote: >>> > (XEN) [ 1408.075638] Xen call trace: >>> > (XEN) [ 1408.079322] [<ffff82d0801ea2a2>] vmx_vmcs_reload+0x32/0x50 >>> > (XEN) [ 1408.086303] [<ffff82d08016c58d>] context_switch+0x85d/0xeb0 >>> > (XEN) [ 1408.093380] [<ffff82d08012fb8e>] >>> > schedule.c#schedule+0x46e/0x7d0 >>> > (XEN) [ 1408.100942] [<ffff82d080164305>] reprogram_timer+0x75/0xe0 >>> > (XEN) [ 1408.107925] [<ffff82d080136400>] > timer.c#timer_softirq_action+0x90/0x210 >>> > (XEN) [ 1408.116263] [<ffff82d08013311c>] >>> > softirq.c#__do_softirq+0x5c/0x90 >>> > (XEN) [ 1408.123921] [<ffff82d080167d35>] domain.c#idle_loop+0x25/0x60 >>> >>> Taking your later reply into account - were you able to figure out >>> what other party held onto the VMCS being waited for here? >> >> Unfortunately, no. It was unclear from debug logs. But judging from >> the following vmx_do_resume() code: >> >> if ( v->arch.hvm_vmx.active_cpu == smp_processor_id() ) >> { >> if ( v->arch.hvm_vmx.vmcs_pa != this_cpu(current_vmcs) ) >> vmx_load_vmcs(v); >> } >> >> If both of the above conditions are true then vmx_vmcs_reload() will >> probably hang. > > I don't follow (reload should run before this, not after), but I must > be missing something more general anyway, as I'm seeing the code > above being needed despite the reload additions. I think I've understood part of it over lunch: Surprisingly enough vmx_ctxt_switch_to() doesn't re-establish the VMCS, so it needs to be done here. Which I think means we don't need the new hook at all, as that way the state is no different between going through ->to() or bypassing it. What I continue to not understand is why vmcs_pa would ever not match current_vmcs when active_cpu is smp_processor_id(). So far I thought both are always updated together. Looking further ... Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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