linux-kernel - Re: Hang on reboot in multi-core FreeBSD guest on Linux KVM host with Intel Sierra Forest CPU

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Message-ID: <CAMGffEmin4HAwoQUjkkoq+_z0sherZcCnkXgMu4PahnM8UmO+A@mail.gmail.com>
Date: Thu, 9 Oct 2025 14:36:03 +0200
From: Jinpu Wang <jinpu.wang@...os.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: fanwenyi0529@...il.com, kvm@...r.kernel.org, 
	Paolo Bonzini <pbonzini@...hat.com>, Xiaoyao Li <xiaoyao.li@...el.com>, linux-kernel@...r.kernel.org, 
	vkuznets@...hat.com
Subject: Re: Hang on reboot in multi-core FreeBSD guest on Linux KVM host with
 Intel Sierra Forest CPU

On Thu, Oct 9, 2025 at 1:21 PM Jinpu Wang <jinpu.wang@...os.com> wrote:
>
> On Thu, Oct 9, 2025 at 5:44 AM Jinpu Wang <jinpu.wang@...os.com> wrote:
> >
> > Hi Sean,
> >
> > On Wed, Oct 8, 2025 at 5:55 PM Sean Christopherson <seanjc@...gle.com> wrote:
> > >
> > > Trimmed Cc: to drop people from the original thread.  In the future, just start
> > > a new bug report.  Piggybacking a 10 year old bug just because the symptoms are
> > > similar does more harm than good.  Whatever the old thread was chasing was already
> > > fixed, _10 years_ ago; they were just trying to identy exactly what commit fixed
> > > the problem.  I.e. whatever they were chasing _can't_ be the same root cause,
> > > because even if it's literally the same code bug, it would require a code change
> > > and thus a regression between v4.0 and v6.1.
> > Thx for the reply,  it makes sense. I will remember this next time.
> > >
> > > On Wed, Oct 08, 2025, Jinpu Wang wrote:
> > > > On Wed, Oct 8, 2025 at 2:44 PM Jack Wang <jinpu.wang@...os.com> wrote:
> > > > > Sorry for bump this old thread, we hit same issue on Intel Sierra Forest
> > > > > machines with LTS kernel 6.1/6.12, maybe KVM comunity could help fix it.
> > >
> > > Are there any host kernels that _do_ work?  E.g. have you tried a bleeding edge
> > > host kernel?
> > I will try linus/master today.
> > >
> > > > > ### **[BUG] Hang on FreeBSD Guest Reboot under KVM on Intel SierraForest (Xeon 6710E)**
> > > > >
> > > > > **Summary:**
> > > > > Multi-cores FreeBSD guests hang during reboot under KVM on systems with
> > > > > Intel(R) Xeon(R) 6710E (SierraForest). The issue is fully reproducible with
> > > > > APICv enabled and disappears when disabling APICv (`enable_apicv=N`). The
> > > > > same configuration works correctly on Ice Lake (Xeon Gold 6338).
> > >
> > > Does Sierra Forest have IPI virtualization?  If so, you could try running with
> > > APICv enabled, but enable_ipiv=false to specifically disable IPI virtualization.
> > Yes, it does:
> > $  grep . /sys/module/kvm_intel/parameters/*
> > /sys/module/kvm_intel/parameters/allow_smaller_maxphyaddr:N
> > /sys/module/kvm_intel/parameters/dump_invalid_vmcs:N
> > /sys/module/kvm_intel/parameters/emulate_invalid_guest_state:Y
> > /sys/module/kvm_intel/parameters/enable_apicv:Y
> > /sys/module/kvm_intel/parameters/enable_ipiv:Y
> > /sys/module/kvm_intel/parameters/enable_shadow_vmcs:Y
> > /sys/module/kvm_intel/parameters/ept:Y
> > /sys/module/kvm_intel/parameters/eptad:Y
> > /sys/module/kvm_intel/parameters/error_on_inconsistent_vmcs_config:Y
> > /sys/module/kvm_intel/parameters/fasteoi:Y
> > /sys/module/kvm_intel/parameters/flexpriority:Y
> > /sys/module/kvm_intel/parameters/nested:Y
> > /sys/module/kvm_intel/parameters/nested_early_check:N
> > /sys/module/kvm_intel/parameters/ple_gap:128
> > /sys/module/kvm_intel/parameters/ple_window:4096
> > /sys/module/kvm_intel/parameters/ple_window_grow:2
> > /sys/module/kvm_intel/parameters/ple_window_max:4294967295
> > /sys/module/kvm_intel/parameters/ple_window_shrink:0
> > /sys/module/kvm_intel/parameters/pml:Y
> > /sys/module/kvm_intel/parameters/preemption_timer:Y
> > /sys/module/kvm_intel/parameters/sgx:N
> > /sys/module/kvm_intel/parameters/unrestricted_guest:Y
> > /sys/module/kvm_intel/parameters/vmentry_l1d_flush:not required
> > /sys/module/kvm_intel/parameters/vnmi:Y
> > /sys/module/kvm_intel/parameters/vpid:Y
> >
> > I tried to disable ipiv, but it doesn't help. freebsd hang on reboot.
> > sudo modprobe -r kvm_intel
> > sudo modprobe  kvm_intel enable_ipiv=N
> > /sys/module/kvm_intel/parameters/enable_ipiv:N
> >
> > Thx!
> +cc Vitaly
> Sorry, I missed one detail, we are use hyper-V enlightment features:
> "+hv-relaxed,+hv-vapic,+hv-time,+hv-runtime,hv-spinlocks=0x1fff,+hv-vpindex,+hv-synic,+hv-stimer,+hv-tlbflush,hv-ipi."
>
> did a lot tests with different features, and looks the hang is related
> to  +hv-synic,+hv-stimer.  hv-synic seems the key which causes boot
> hang of Freebsd 14.
>
> But the problem seems fixed with FreeBSD 15?  I guess it's this fix:
https://reviews.freebsd.org/D43508

>
> Seems it's a bug from freebsd side, rather than on kvm side to me, but
> I'm puzzled by disable apicv helps?
>
> Thx!