linux-kernel - Re: [PATCH v2] x86/xen: don't unbind uninitialized lock_kicker

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Message-ID: <5950df5c-79d6-b2bc-4f2b-35624a3c0d1e@suse.com>
Date:   Mon, 9 Nov 2020 06:34:07 +0100
From:   Jürgen Groß <jgross@...e.com>
To:     Brian Masney <bmasney@...hat.com>, boris.ostrovsky@...cle.com,
        sstabellini@...nel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org, dustymabe@...hat.com
Subject: Re: [PATCH v2] x86/xen: don't unbind uninitialized lock_kicker_irq

On 07.11.20 02:11, Brian Masney wrote:
> When booting a hyperthreaded system with the kernel parameter
> 'mitigations=auto,nosmt', the following warning occurs:
> 
>      WARNING: CPU: 0 PID: 1 at drivers/xen/events/events_base.c:1112 unbind_from_irqhandler+0x4e/0x60
>      ...
>      Hardware name: Xen HVM domU, BIOS 4.2.amazon 08/24/2006
>      ...
>      Call Trace:
>       xen_uninit_lock_cpu+0x28/0x62
>       xen_hvm_cpu_die+0x21/0x30
>       takedown_cpu+0x9c/0xe0
>       ? trace_suspend_resume+0x60/0x60
>       cpuhp_invoke_callback+0x9a/0x530
>       _cpu_up+0x11a/0x130
>       cpu_up+0x7e/0xc0
>       bringup_nonboot_cpus+0x48/0x50
>       smp_init+0x26/0x79
>       kernel_init_freeable+0xea/0x229
>       ? rest_init+0xaa/0xaa
>       kernel_init+0xa/0x106
>       ret_from_fork+0x35/0x40
> 
> The secondary CPUs are not activated with the nosmt mitigations and only
> the primary thread on each CPU core is used. In this situation,
> xen_hvm_smp_prepare_cpus(), and more importantly xen_init_lock_cpu(), is
> not called, so the lock_kicker_irq is not initialized for the secondary
> CPUs. Let's fix this by exiting early in xen_uninit_lock_cpu() if the
> irq is not set to avoid the warning from above for each secondary CPU.
> 
> Signed-off-by: Brian Masney <bmasney@...hat.com>

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen

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