From: Greg KH <gregkh@linuxfoundation.org>
To: Niels Dettenbach <nd@syndicat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
stable@vger.kernel.org
Subject: Re: [PATCH 1/1] x86: SMP broken on Xen PV DomU since 6.9
Date: Thu, 12 Sep 2024 10:51:44 +0200 [thread overview]
Message-ID: <2024091235-degree-drinkable-5363@gregkh> (raw)
In-Reply-To: <5998315.MhkbZ0Pkbq@gongov>
On Thu, Sep 12, 2024 at 10:48:14AM +0200, Niels Dettenbach wrote:
> Virtual machines under Xen Hypervisor (DomU) running in Xen PV mode use a
> special, nonstandard synthetized CPU topology which "just works" under
> kernels 6.9.x while newer kernels wrongly assuming a "crash kernel" and
> disable SMP (reducing to one CPU core) because the newer topology
> implementation produces a wrong error "[Firmware Bug]: APIC enumeration
> order not specification compliant" after new topology checks which are
> improper for Xen PV platform. As a result, the kernel disables SMT and
> activates just one CPU core within the VM (DomU).
>
> The patch disables the regarding checks if it is running in Xen PV
> mode (only) and bring back SMP / all CPUs as in the past to such DomU
> VMs.
>
> Signed-off-by: Niels Dettenbach <nd@syndicat.com>
>
> ---
>
>
> The current behaviour leads all of our production Xen Host platforms
> (amd64 - HPE proliant) unusable after updating to newer linux kernels
> (with just one CPU available/activated per VM) while older kernels and
> other OS (current NetBSD PV DomU) still work fully (and stable since many
> years on the platform).
>
> Xen PV mode is still provided by current Xen and widely used - even
> if less wide as the newer Xen PVH mode today. So a solution probably
> will be required.
>
> So we assume that bug affects stable@vger.kernel.org as well.
>
<formletter>
This is not the correct way to submit patches for inclusion in the
stable kernel tree. Please read:
https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.
</formletter>
prev parent reply other threads:[~2024-09-12 8:51 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-09-12 8:48 [PATCH 1/1] x86: SMP broken on Xen PV DomU since 6.9 Niels Dettenbach
2024-09-12 8:51 ` Greg KH [this message]
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