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: <aOaJbHPBXHwxlC1S@google.com>
Date: Wed, 8 Oct 2025 08:55:24 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Jinpu Wang <jinpu.wang@...os.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
Subject: Re: Hang on reboot in multi-core FreeBSD guest on Linux KVM host with
 Intel Sierra Forest CPU

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.

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?

> > ### **[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.