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Differential D37227

vmm: do not leak halted_cpus bit after suspension
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Authored by kib on Oct 31 2022, 11:33 PM.
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bz
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rG4d447b30f7be: vmm: do not leak halted_cpus bit after suspension
Summary

Reported by: bz
PR: 267468

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rG FreeBSD src repository
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kib created this revision.Oct 31 2022, 11:33 PM
Herald added a reviewer: bhyve. · View Herald TranscriptOct 31 2022, 11:33 PM
Herald added subscribers: bcran, rgrimes, imp. · View Herald Transcript
kib requested review of this revision.Oct 31 2022, 11:33 PM
emaste added a subscriber: emaste.Nov 1 2022, 12:08 PM
markj accepted this revision as: markj.Nov 1 2022, 2:13 PM
markj added inline comments.
sys/amd64/vmm/vmm.c
1408

If there are two vcpus, and one is already halted, then we may suspend the VM here. Then the halted vcpu thread can wake up and handle a signal, so the VM will be suspended but halted_cpus != active_cpus. Hmm, but vmx_run() and svm_run() will return VM_EXITCODE_SUSPENDED once the vcpu tries to continue executing the (suspended) guest, so this seems ok.

This revision is now accepted and ready to land.Nov 1 2022, 2:13 PM
kib added inline comments.Nov 1 2022, 2:49 PM
sys/amd64/vmm/vmm.c
1408

When adding this patch, I wondered if clearing of the bit in halted_cpus should be done under vcpu spin lock. But it seems that vm_resume_cpu() does not care, so I did not do locked the spin lock in the error path as well.

I suspect that vm_suspend() in fact needs more synchronization there, regardless of my fix.

Closed by commit rG4d447b30f7be: vmm: do not leak halted_cpus bit after suspension (authored by kib). · Explain WhyNov 1 2022, 9:01 PM
This revision was automatically updated to reflect the committed changes.
kib added a commit: rG4d447b30f7be: vmm: do not leak halted_cpus bit after suspension.

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sys/
amd64/
vmm/
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sys/amd64/vmm/vmm.c

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