linux-kernel - Re: [PATCH] arm: Add support for ZSTD compressed kernel

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Message-ID: <20200806101145.GC1551@shell.armlinux.org.uk>
Date:   Thu, 6 Aug 2020 11:11:45 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Norbert Lange <nolange79@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Petr Malat <oss@...at.biz>, Kees Cook <keescook@...omium.org>,
        Adam Borowski <kilobyte@...band.pl>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Terrell <terrelln@...com>
Subject: Re: [PATCH] arm: Add support for ZSTD compressed kernel

On Thu, Aug 06, 2020 at 10:45:42AM +0200, Norbert Lange wrote:
> Am Do., 6. Aug. 2020 um 02:30 Uhr schrieb Russell King - ARM Linux
> admin <linux@...linux.org.uk>:
> >
> > On Thu, Aug 06, 2020 at 01:05:55AM +0200, Norbert Lange wrote:
> > > diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
> > > index 434a16982e34..1af01bfe6638 100644
> > > --- a/arch/arm/boot/compressed/head.S
> > > +++ b/arch/arm/boot/compressed/head.S
> > > @@ -614,7 +614,11 @@ not_relocated:   mov     r0, #0
> > >   */
> > >               mov     r0, r4
> > >               mov     r1, sp                  @ malloc space above stack
> > > +#if defined(CONFIG_KERNEL_ZSTD)
> > > +             add     r2, sp, #0x30000        @ Context needs ~160K
> >
> > That's going to mess up kexec:
> >
> >         /*
> >          * The zImage length does not include its stack (4k) or its
> >          * malloc space (64k).  Include this.
> >          */
> >         len += 0x11000;
> >
> > I guess we need to add this to the information provided to kexec.
> 
> Ouch, I guess it's rather impossible to load a new ZSTD kernel with a old
> kexec version in that case.
> 
> Some ideas to fix that would be:
> 
> -   Increase the padding to "192K + 4K is enough for everyone" in kexec
> -   Add the required/recommended stack+heap size to zImage so kexec can use it.

This is definitely preferred.  See patches - though this is only the
kernel side.  The first I've had for some time and isn't related to
this issue.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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