Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [RFC PATCH 00/26] Runtime paravirt patching | Date | Wed, 08 Apr 2020 16:12:58 +0200 |
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Ankur Arora <ankur.a.arora@oracle.com> writes: > A KVM host (or another hypervisor) might advertise paravirtualized > features and optimization hints (ex KVM_HINTS_REALTIME) which might > become stale over the lifetime of the guest. For instance, the > host might go from being undersubscribed to being oversubscribed > (or the other way round) and it would make sense for the guest > switch pv-ops based on that.
If your host changes his advertised behaviour then you want to fix the host setup or find a competent admin.
> This lockorture splat that I saw on the guest while testing this is > indicative of the problem: > > [ 1136.461522] watchdog: BUG: soft lockup - CPU#8 stuck for 22s! [lock_torture_wr:12865] > [ 1136.461542] CPU: 8 PID: 12865 Comm: lock_torture_wr Tainted: G W L 5.4.0-rc7+ #77 > [ 1136.461546] RIP: 0010:native_queued_spin_lock_slowpath+0x15/0x220 > > (Caused by an oversubscribed host but using mismatched native pv_lock_ops > on the gues.)
And this illustrates what? The fact that you used a misconfigured setup.
> This series addresses the problem by doing paravirt switching at > runtime.
You're not addressing the problem. Your fixing the symptom, which is wrong to begin with.
> The alternative use-case is a runtime version of apply_alternatives() > (not posted with this patch-set) that can be used for some safe subset > of X86_FEATUREs. This could be useful in conjunction with the ongoing > late microcode loading work that Mihai Carabas and others have been > working on.
This has been discussed to death before and there is no safe subset as long as this hasn't been resolved:
https://lore.kernel.org/lkml/alpine.DEB.2.21.1909062237580.1902@nanos.tec.linutronix.de/
Thanks,
tglx
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