linux-kernel - Re: [PATCH v12 13/16] arm64: kexec_file: invoke the kernel without purgatory

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Message-ID: <20180727072242.GH11258@linaro.org>
Date:   Fri, 27 Jul 2018 16:22:43 +0900
From:   AKASHI Takahiro <takahiro.akashi@...aro.org>
To:     James Morse <james.morse@....com>
Cc:     catalin.marinas@....com, will.deacon@....com, dhowells@...hat.com,
        vgoyal@...hat.com, herbert@...dor.apana.org.au,
        davem@...emloft.net, dyoung@...hat.com, bhe@...hat.com,
        arnd@...db.de, schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
        ard.biesheuvel@...aro.org, bhsharma@...hat.com,
        kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 13/16] arm64: kexec_file: invoke the kernel without
 purgatory

On Thu, Jul 26, 2018 at 02:36:07PM +0100, James Morse wrote:
> Hi Akashi,
> 
> On 24/07/18 07:57, AKASHI Takahiro wrote:
> > On arm64, purgatory would do almost nothing. So just invoke secondary
> > kernel directly by jumping into its entry code.
> > 
> > While, in this case, cpu_soft_restart() must be called with dtb address
> > in the fifth argument, the behavior still stays compatible with kexec_load
> > case as long as the argument is null.
> 
> This patch conflicts with commit 76f4e2da45b4 ("arm64: kexec: always reset to
> EL2 if present") in the arm64 tree.

I haven't noticed Mark's patch.

I'm going to have to refresh my memory regarding why I introduced
el2_switch when I implemented kdump.
According to my current memory, however, I added
kvm_arch_hardware_enable/disable(), and associated functions, to gracefully
shutdown EL2 in case of kexec. Since we have no chance to call reset
function (via notifier) at kdump, I believed that el2_switch was necessary
for better chance of successful kdump.

Thanks,
-Takahiro AKASHI

> Thanks,
> 
> James
> 
> > diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
> > index f76ea92dff91..830a5063e09d 100644
> > --- a/arch/arm64/kernel/machine_kexec.c
> > +++ b/arch/arm64/kernel/machine_kexec.c
> > @@ -205,10 +205,18 @@ void machine_kexec(struct kimage *kimage)
> >  	 * uses physical addressing to relocate the new image to its final
> >  	 * position and transfers control to the image entry point when the
> >  	 * relocation is complete.
> > +	 * In kexec case, kimage->start points to purgatory assuming that
> > +	 * kernel entry and dtb address are embedded in purgatory by
> > +	 * userspace (kexec-tools).
> > +	 * In kexec_file case, the kernel starts directly without purgatory.
> >  	 */
> > -
> >  	cpu_soft_restart(kimage != kexec_crash_image,
> > -		reboot_code_buffer_phys, kimage->head, kimage->start, 0);
> > +		reboot_code_buffer_phys, kimage->head, kimage->start,
> > +#ifdef CONFIG_KEXEC_FILE
> > +						kimage->arch.dtb_mem);
> > +#else
> > +						0);
> > +#endif
> >  
> >  	BUG(); /* Should never get here. */
> >  }