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From:   =?UTF-8?B?6buE5p2w?= <huangjie.albert@bytedance.com>
Date:   Mon, 25 Jul 2022 21:30:41 +0800
Message-ID: <CABKxMyNj7Oo3X47APa8Ro-CCK3=XFogorJ2maTCstgsrrC28kg@mail.gmail.com>
Subject: Re: [External] Re: [PATCH 1/4] kexec: reuse crash kernel reserved
 memory for normal kexec
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Nick Desaulniers <ndesaulniers@google.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Michael Roth <michael.roth@amd.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Joerg Roedel <jroedel@suse.de>,
        Mark Rutland <mark.rutland@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Sean Christopherson <seanjc@google.com>,
        Kees Cook <keescook@chromium.org>,
        linux-kernel@vger.kernel.org, kexec@lists.infradead.org,
        linux-kbuild@vger.kernel.org
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Jason A. Donenfeld <Jason@zx2c4.com> =E4=BA=8E2022=E5=B9=B47=E6=9C=8825=E6=
=97=A5=E5=91=A8=E4=B8=80 20:02=E5=86=99=E9=81=93=EF=BC=9A
>
> Hi Albert,
>
> On Mon, Jul 25, 2022 at 04:38:53PM +0800, Albert Huang wrote:
> > The kexec userspace tool also needs to add parameter options(-r) that
> > support the use of reserved memory (see another patch for kexec)
> >
> > [...]
> >
> > -     if (kexec_on_panic) {
> > +     if (kexec_on_panic && kexec_on_reserved) {
>
> Two small questions related to this:
>
> - Why does kexec-tools need an option, or more specifically, why does
>   userspace need to communicate about this at all? Can't the kernel just
>   automatically use the available reserved memory in the case that's not
>   already being used by the panic handler kernel? I'm curious about
>   whether there are caveats that would make this occasionally
>   undesirable, hence suggesting an option.

Because the crash kernel will also use this part of the memory,
so do not use this mechanism unless explicitly specified. So I tend to
add an option

>
> - I don't totally understand how this works, so I might be a bit off
>   here, but is there any chance that this could be made to co-exist with
>   kexec_on_panic? Can a larger region just be reserved, specifically for
>   this, rather than piggy backing on the panic handler region?
>
> > +static struct page *kimage_alloc_reserverd_control_pages(struct kimage=
 *image,
> > +     case KEXEC_TYPE_RESERVED_MEM:
> > +             pages =3D kimage_alloc_reserverd_control_pages(image, ord=
er);
>
> Nit:
>   reserverd -> reserved

thanks for that, I will correct it

>
> Jason