linux-kernel - Re: [PATCH] kexec: do syscore_shutdown() in kernel

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Date:   Wed, 13 Dec 2023 10:39:52 -0600
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     James Gowans <jgowans@...zon.com>
Cc:     "Sean Christopherson" <seanjc@...gle.com>,
        <kexec@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Marc Zyngier <maz@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Tony Luck <tony.luck@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        "Pavel Machek" <pavel@....cz>, Sebastian Reichel <sre@...nel.org>,
        Orson Zhai <orsonzhai@...il.com>,
        Alexander Graf <graf@...zon.de>,
        "Jan H . Schoenherr" <jschoenh@...zon.de>
Subject: Re: [PATCH] kexec: do syscore_shutdown() in kernel_kexec

James Gowans <jgowans@...zon.com> writes:

> syscore_shutdown() runs driver and module callbacks to get the system
> into a state where it can be correctly shut down. In commit
> 6f389a8f1dd2 ("PM / reboot: call syscore_shutdown() after disable_nonboot_cpus()")
> syscore_shutdown() was removed from kernel_restart_prepare() and hence
> got (incorrectly?) removed from the kexec flow. This was innocuous until
> commit 6735150b6997 ("KVM: Use syscore_ops instead of reboot_notifier to hook restart/shutdown")
> changed the way that KVM registered its shutdown callbacks, switching from
> reboot notifiers to syscore_ops.shutdown. As syscore_shutdown() is
> missing from kexec, KVM's shutdown hook is not run and virtualisation is
> left enabled on the boot CPU which results in triple faults when
> switching to the new kernel on Intel x86 VT-x with VMXE enabled.
>
> Fix this by adding syscore_shutdown() to the kexec sequence. In terms of
> where to add it, it is being added after migrating the kexec task to the
> boot CPU, but before APs are shut down. It is not totally clear if this
> is the best place: in commit 6f389a8f1dd2 ("PM / reboot: call syscore_shutdown() after disable_nonboot_cpus()")
> it is stated that "syscore_ops operations should be carried with one
> CPU on-line and interrupts disabled." APs are only offlined later in
> machine_shutdown(), so this syscore_shutdown() is being run while APs
> are still online. This seems to be the correct place as it matches where
> syscore_shutdown() is run in the reboot and halt flows - they also run
> it before APs are shut down. The assumption is that the commit message
> in commit 6f389a8f1dd2 ("PM / reboot: call syscore_shutdown() after disable_nonboot_cpus()")
> is no longer valid.
>
> KVM has been discussed here as it is what broke loudly by not having
> syscore_shutdown() in kexec, but this change impacts more than just KVM;
> all drivers/modules which register a syscore_ops.shutdown callback will
> now be invoked in the kexec flow. Looking at some of them like x86 MCE
> it is probably more correct to also shut these down during kexec.
> Maintainers of all drivers which use syscore_ops.shutdown are added on
> CC for visibility. They are:
>
> arch/powerpc/platforms/cell/spu_base.c  .shutdown = spu_shutdown,
> arch/x86/kernel/cpu/mce/core.c	        .shutdown = mce_syscore_shutdown,
> arch/x86/kernel/i8259.c                 .shutdown = i8259A_shutdown,
> drivers/irqchip/irq-i8259.c	        .shutdown = i8259A_shutdown,
> drivers/irqchip/irq-sun6i-r.c	        .shutdown = sun6i_r_intc_shutdown,
> drivers/leds/trigger/ledtrig-cpu.c	.shutdown = ledtrig_cpu_syscore_shutdown,
> drivers/power/reset/sc27xx-poweroff.c	.shutdown = sc27xx_poweroff_shutdown,
> kernel/irq/generic-chip.c	        .shutdown = irq_gc_shutdown,
> virt/kvm/kvm_main.c	                .shutdown = kvm_shutdown,
>
> This has been tested by doing a kexec on x86_64 and aarch64.

>From the 10,000 foot perspective:
Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>


Eric

> Fixes: 6735150b6997 ("KVM: Use syscore_ops instead of reboot_notifier to hook restart/shutdown")
>
> Signed-off-by: James Gowans <jgowans@...zon.com>
> Cc: Eric Biederman <ebiederm@...ssion.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Sean Christopherson <seanjc@...gle.com>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Tony Luck <tony.luck@...el.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Chen-Yu Tsai <wens@...e.org>
> Cc: Jernej Skrabec <jernej.skrabec@...il.com>
> Cc: Samuel Holland <samuel@...lland.org>
> Cc: Pavel Machek <pavel@....cz>
> Cc: Sebastian Reichel <sre@...nel.org>
> Cc: Orson Zhai <orsonzhai@...il.com>
> Cc: Alexander Graf <graf@...zon.de>
> Cc: Jan H. Schoenherr <jschoenh@...zon.de>
> ---
>  kernel/kexec_core.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index be5642a4ec49..b926c4db8a91 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -1254,6 +1254,7 @@ int kernel_kexec(void)
>  		kexec_in_progress = true;
>  		kernel_restart_prepare("kexec reboot");
>  		migrate_to_reboot_cpu();
> +		syscore_shutdown();
>  
>  		/*
>  		 * migrate_to_reboot_cpu() disables CPU hotplug assuming that