Messages in this thread | | | Date | Fri, 9 Nov 2018 10:42:37 -0800 | From | Sean Christopherson <> | Subject | Re: x86_64 INIT/SIPI Bug |
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On Fri, Nov 09, 2018 at 11:04:59AM -0700, Rian Quinn wrote: > >> I apologize upfront if this is the wrong place to post this, pretty new to this. > >> > >> We are working on the Bareflank Hypervisor (www.bareflank.org), and we > >> are passing through the INIT/SIPI process (similar to how a VMX > >> rootkit from EFI might boot the OS) and we noticed that on Arch Linux, > >> the INIT/SIPI process stalls, something we are not seeing on Ubuntu. > > > > I'm confused, INIT is blocked post-VMXON, what are you passing through? > > You are correct that INIT will track unconditionally, but all we do is set the > activity state to wait-for-sipi and return back, allowing Linux to continue > its boot process.
That's not pass-through, maybe call it reflection? I realize I'm being a bit pedantic, but differentiating between the two matters since true pass-through gives you bare metal performance whereas reflection obviously requires a round-trip VMX transition.
Most hypervisors don't need a delay because they don't pass-through the local APIC and instead emulate INIT/SIPI/SIPI. In other words, forcing a delay for all hypervisors is unwarranted.
The correct fix is probably to add a new hook to struct x86_hyper_init to provide a custom init delay, and add Bareflank as a new hypervisor.
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