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Message-ID: <aJojDiHWi8cgvA2W@pie>
Date: Mon, 11 Aug 2025 17:06:22 +0000
From: Yao Zi <ziyao@...root.org>
To: Youling Tang <youling.tang@...ux.dev>,
Huacai Chen <chenhuacai@...nel.org>
Cc: WANG Xuerui <kernel@...0n.name>, Baoquan He <bhe@...hat.com>,
kexec@...ts.infradead.org, loongarch@...ts.linux.dev,
linux-kernel@...r.kernel.org, Youling Tang <tangyouling@...inos.cn>
Subject: Re: [PATCH 2/6] LoongArch: Add kexec_file support
On Mon, Aug 11, 2025 at 05:26:55PM +0800, Youling Tang wrote:
> From: Youling Tang <tangyouling@...inos.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@...inos.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/include/asm/image.h b/arch/loongarch/include/asm/image.h
> index 1f090736e71d..829e1ecb1f5d 100644
> --- a/arch/loongarch/include/asm/image.h
> +++ b/arch/loongarch/include/asm/image.h
> @@ -36,5 +36,23 @@ struct loongarch_image_header {
> uint32_t pe_header;
> };
>
> +static const uint8_t loongarch_image_pe_sig[2] = {'M', 'Z'};
> +static const uint8_t loongarch_pe_machtype[6] = {'P', 'E', 0x0, 0x0, 0x64, 0x62};
loongarch_pe_machtype isn't used at all.
> +
> +/**
> + * loongarch_header_check_pe_sig - Helper to check the loongarch image header.
> + *
> + * Returns non-zero if 'MZ' signature is found.
> + */
> +
> +static inline int loongarch_header_check_pe_sig(const struct loongarch_image_header *h)
> +{
> + if (!h)
> + return 0;
> +
> + return (h->pe_sig[0] == loongarch_image_pe_sig[0]
> + && h->pe_sig[1] == loongarch_image_pe_sig[1]);
This could be simplified with a memcmp(). Also, this check isn't strict
enough: PE files for any architectures, and even legacy MS-DOS COM
executables all start with "MZ".
> +}
> +
> #endif /* __ASSEMBLY__ */
> #endif /* __ASM_IMAGE_H */
...
> 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@...inos.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.
> + 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;
> +}
> +
> +static void *image_load(struct kimage *image,
> + char *kernel, unsigned long kernel_len,
> + char *initrd, unsigned long initrd_len,
> + char *cmdline, unsigned long cmdline_len)
> +{
> + struct loongarch_image_header *h;
> + struct kexec_buf kbuf;
> + unsigned long text_offset, kernel_segment_number;
> + struct kexec_segment *kernel_segment;
> + int ret;
> +
> + h = (struct loongarch_image_header *)kernel;
> + if (!h->image_size)
> + return ERR_PTR(-EINVAL);
> +
> + /* Load the kernel */
> + kbuf.image = image;
> + kbuf.buf_min = 0;
> + kbuf.buf_max = ULONG_MAX;
> + kbuf.top_down = false;
> +
> + kbuf.buffer = kernel;
> + kbuf.bufsz = kernel_len;
> + kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
> + kbuf.memsz = le64_to_cpu(h->image_size);
> + text_offset = le64_to_cpu(h->text_offset);
> + kbuf.buf_align = SZ_2M;
I think this aligment is unnecessary for relocatable LoongArch kernels:
it should be enough to align to the page size. See also my comments
below.
> + kernel_segment_number = image->nr_segments;
> +
> + /*
> + * The location of the kernel segment may make it impossible to satisfy
> + * the other segment requirements, so we try repeatedly to find a
> + * location that will work.
> + */
> + while ((ret = kexec_add_buffer(&kbuf)) == 0) {
> + /* Try to load additional data */
> + kernel_segment = &image->segment[kernel_segment_number];
> + ret = load_other_segments(image, kernel_segment->mem,
> + kernel_segment->memsz, initrd,
> + initrd_len, cmdline, cmdline_len);
> + if (!ret)
> + break;
> +
> + /*
> + * We couldn't find space for the other segments; erase the
> + * kernel segment and try the next available hole.
> + */
> + image->nr_segments -= 1;
> + kbuf.buf_min = kernel_segment->mem + kernel_segment->memsz;
> + kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
> + }
> +
> + if (ret) {
> + pr_err("Could not find any suitable kernel location!");
> + return ERR_PTR(ret);
> + }
> +
> + kernel_segment = &image->segment[kernel_segment_number];
> +
> + /* Make sure the second kernel jumps to the correct "kernel_entry". */
> + image->start = kernel_segment->mem + h->kernel_entry - text_offset;
A non-relocatable loongarch kernel cannot be loaded to arbitrary
address. Thus this loading function seems to only work for relocatable
kernels, maybe it's better to leave a comment indicating the limitation.
For now, we don't seem to have a way to find out whether the kernel is
relocatable (for example, a flag in kernel image header), so it's
impossible to point out whether the loaded kernel boots fine with
arbitrary loading address...
> + kexec_dprintk("Loaded kernel at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
> + kernel_segment->mem, kbuf.bufsz,
> + kernel_segment->memsz);
> +
> + return NULL;
> +}
> +
> +const struct kexec_file_ops kexec_image_ops = {
> + .probe = image_probe,
> + .load = image_load,
> +};
> 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).
> 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
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