Re: kexec on arm fails, possibly due to memdup_user

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Amr Bekhit <amr@helmpcb.com>
Cc: linux-arm-kernel@lists.infradead.org
Subject: Re: kexec on arm fails, possibly due to memdup_user
Date: Tue, 4 Jul 2023 21:53:32 +0100	[thread overview]
Message-ID: <ZKSGzJl0kwGiu4Pc@shell.armlinux.org.uk> (raw)
In-Reply-To: <CAHmAUHL9Cfkq0JyNMv-HpY+VUZYSj8vQ-SN7BGjtpY36R6OrKA@mail.gmail.com>

On Tue, Jul 04, 2023 at 06:48:26PM +0100, Amr Bekhit wrote:
> > It could be:
> >
> >         /*
> >          * Validate that if the current HW supports SMP, then the SW supports
> >          * and implements CPU hotplug for the current HW. If not, we won't be
> >          * able to kexec reliably, so fail the prepare operation.
> >          */
> >         if (num_possible_cpus() > 1 && platform_can_secondary_boot() &&
> >             !platform_can_cpu_hotplug())
> >                 return -EINVAL;
> 
> Thanks - this was exactly the issue. memdup_user was a red herring
> caused by some missing printk's due to me not adding newlines. It's
> now clear that for my CPU (IPQ4019), the cpu_kill function is not
> implemented in the smp_operations struct.
> 
> Looking online, I was able to see that kexec does work on my cpu as
> long as nr_cpus=1 is specified in the kernel command line (see
> https://patchwork.kernel.org/project/linux-arm-msm/patch/CAAGQ2nQNQ-aFkcrQHNA6H5TZ1tTovtfO_0Ohfndn9jXy13Hc6A@mail.gmail.com/#22064531).
> 
> I've tried this myself, and indeed setting this option allows the
> kexec load to perform successfully. However, when I run kexec -e,
> after the "Bye!" message the system just hangs and reboots after a
> while, presumably due to a watchdog timeout:
> 
> ~ # kexec -d --dtb=/data/image-qcom-ipq4019-nerd.dtb -l /data/zImage-openwrt
...
> Any pointers as to what could be wrong at this point?

Try without --dtb

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel