Re: [PATCH 2/6] LoongArch: Add kexec_file support

[Yao Zi <ziyao@disroot.org>]

On Tue, Aug 12, 2025 at 10:39:59AM +0800, Huacai Chen wrote:
> On Tue, Aug 12, 2025 at 1:09 AM Yao Zi <ziyao@disroot.org> wrote:
> >
> > On Mon, Aug 11, 2025 at 05:26:55PM +0800, Youling Tang wrote:
> > > From: Youling Tang <tangyouling@kylinos.cn>
> > >
> > > This patch adds support for kexec_file on LoongArch.
> > >
> > > The image_load() as two parts:
> > > - the first part loads the kernel image (vmlinuz.efi or vmlinux.efi)
> > > - the second part loads other segments (eg: initrd, cmdline)
> > >
> > > Currently, pez(vmlinuz.efi) and pei(vmlinux.efi) format images are supported,
> > > but ELF format is not supported.
> > >
> > > Signed-off-by: Youling Tang <tangyouling@kylinos.cn>
> > > ---
> > >  arch/loongarch/Kconfig                     |   8 ++
> > >  arch/loongarch/include/asm/image.h         |  18 ++++
> > >  arch/loongarch/include/asm/kexec.h         |  12 +++
> > >  arch/loongarch/kernel/Makefile             |   1 +
> > >  arch/loongarch/kernel/kexec_image.c        | 112 +++++++++++++++++++++
> > >  arch/loongarch/kernel/machine_kexec.c      |  33 ++++--
> > >  arch/loongarch/kernel/machine_kexec_file.c |  46 +++++++++
> > >  7 files changed, 219 insertions(+), 11 deletions(-)
> > >  create mode 100644 arch/loongarch/kernel/kexec_image.c
> > >  create mode 100644 arch/loongarch/kernel/machine_kexec_file.c
> >
> > > diff --git a/arch/loongarch/kernel/kexec_image.c b/arch/loongarch/kernel/kexec_image.c
> > > new file mode 100644
> > > index 000000000000..fdd1845b4e2e
> > > --- /dev/null
> > > +++ b/arch/loongarch/kernel/kexec_image.c
> > > @@ -0,0 +1,112 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +/*
> > > + * Kexec image loader for LoongArch
> > > +
> > > + * Author: Youling Tang <tangyouling@kylinos.cn>
> > > + * Copyright (C) 2025 KylinSoft Corporation.
> > > + */
> > > +
> > > +#define pr_fmt(fmt)  "kexec_file(Image): " fmt
> > > +
> > > +#include <linux/err.h>
> > > +#include <linux/errno.h>
> > > +#include <linux/kernel.h>
> > > +#include <linux/kexec.h>
> > > +#include <linux/pe.h>
> > > +#include <linux/string.h>
> > > +#include <asm/byteorder.h>
> > > +#include <asm/cpufeature.h>
> > > +#include <asm/image.h>
> > > +
> > > +static int image_probe(const char *kernel_buf, unsigned long kernel_len)
> > > +{
> > > +     const struct loongarch_image_header *h =
> > > +             (const struct loongarch_image_header *)(kernel_buf);
> >
> > Parentheses around "kernel_buf" are unnecessary.
> >
> > > +     if (!h || (kernel_len < sizeof(*h))) {
> >
> > Comparisons have higher priority than logic operations, so this pair of
> > parentheses is redundant, too.
> But the kernel coding style suggest to use parentheses in this case.

Could you please quote the original text? I have read through
Documentation/process/coding-style.rst again but didn't find similar
suggestions...

And git grep '[[:alnum:]]\+ || [[:alnum:]_]\+ [<>]=\?' results in more
than 7000 matches, including 25 in arch/loongarch...

Anyway, this is a little nitpick. I'm just pointing out the expression
is equal to "!h || kernel_len < sizeof(*h)", and whether it's simplified
is fine to me.

> >
> > > +             pr_err("No loongarch image header.\n");
> > > +             return -EINVAL;
> > > +     }
> > > +
> > > +     if (!loongarch_header_check_pe_sig(h)) {
> > > +             pr_err("Bad loongarch PE image header.\n");
> > > +             return -EINVAL;
> > > +     }
> > > +
> > > +     return 0;
> > > +}

...

> > > diff --git a/arch/loongarch/kernel/machine_kexec.c b/arch/loongarch/kernel/machine_kexec.c
> > > index f9381800e291..008f43e26120 100644
> > > --- a/arch/loongarch/kernel/machine_kexec.c
> > > +++ b/arch/loongarch/kernel/machine_kexec.c
> > > @@ -70,18 +70,28 @@ int machine_kexec_prepare(struct kimage *kimage)
> >
> > ...
> >
> > > -     if (!kimage->arch.cmdline_ptr) {
> > > -             pr_err("Command line not included in the provided image\n");
> > > -             return -EINVAL;
> > > +             if (!kimage->arch.cmdline_ptr) {
> > > +                     pr_err("Command line not included in the provided image\n");
> > > +                     return -EINVAL;
> > > +             }
> > >       }
> > >
> > >       /* kexec/kdump need a safe page to save reboot_code_buffer */
> > > @@ -288,7 +298,8 @@ void machine_kexec(struct kimage *image)
> > >       local_irq_disable();
> > >
> > >       pr_notice("EFI boot flag 0x%lx\n", efi_boot);
> > > -     pr_notice("Command line at 0x%lx\n", cmdline_ptr);
> > > +     pr_notice("Command line addr at 0x%lx\n", cmdline_ptr);
> > > +     pr_notice("Command line at %s\n", (char *)cmdline_ptr);
> >
> > The printed message doesn't match meaning of the pointer: you're
> > printing the content of cmdline_ptr, instead of its address, thus
> > "Command line at" sounds confusing to me.
> >
> > Furthermore, this chunk isn't related to "support for kexec_file", I
> > think it's better to separate it into another patch (or even another
> > series).
> Separating is not necessary from my point of view, indeed I suggest to
> squash patches in this series.

I realized this comment is a little nitpicking, too, so I'm going to say
either is fine to me.

> Huacai

Best regards,
Yao Zi

> >
> > >       pr_notice("System table at 0x%lx\n", systable_ptr);
> > >       pr_notice("We will call new kernel at 0x%lx\n", start_addr);
> > >       pr_notice("Bye ...\n");
> >
> > Best regards,
> > Yao Zi
>