Re: [PATCH v17 02/10] of: Add a common kexec FDT setup function

Thiago Jung Bauermann
2021-02-12T01:12:33Z

There's actually a complication that I just noticed and needs to be
addressed. More below.

Lakshmi Ramasubramanian <nramas@linux.microsoft.com> writes:

> From: Rob Herring <robh@kernel.org>
>
> Both arm64 and powerpc do essentially the same FDT /chosen setup for
> kexec. The differences are either omissions that arm64 should have
> or additional properties that will be ignored. The setup code can be
> combined and shared by both powerpc and arm64.
>
> The differences relative to the arm64 version:
> - If /chosen doesn't exist, it will be created (should never happen).
> - Any old dtb and initrd reserved memory will be released.
> - The new initrd and elfcorehdr are marked reserved.
> - "linux,booted-from-kexec" is set.
>
> The differences relative to the powerpc version:
> - "kaslr-seed" and "rng-seed" may be set.
> - "linux,elfcorehdr" is set.
> - Any existing "linux,usable-memory-range" is removed.
>
> Combine the code for setting up the /chosen node in the FDT and updating
> the memory reservation for kexec, for powerpc and arm64, in
> of_kexec_alloc_and_setup_fdt() and move it to "drivers/of/kexec.c".
>
> Signed-off-by: Rob Herring <robh@kernel.org>
> Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
> ---
> drivers/of/Makefile | 6 ++
> drivers/of/kexec.c | 258 ++++++++++++++++++++++++++++++++++++++++++++
> include/linux/of.h | 13 +++
> 3 files changed, 277 insertions(+)
> create mode 100644 drivers/of/kexec.c
>
> diff --git a/drivers/of/Makefile b/drivers/of/Makefile
> index 6e1e5212f058..c13b982084a3 100644
> --- a/drivers/of/Makefile
> +++ b/drivers/of/Makefile
> @@ -14,4 +14,10 @@ obj-$(CONFIG_OF_RESOLVE) += resolver.o
> obj-$(CONFIG_OF_OVERLAY) += overlay.o
> obj-$(CONFIG_OF_NUMA) += of_numa.o
>
> +ifdef CONFIG_KEXEC_FILE
> +ifdef CONFIG_OF_FLATTREE
> +obj-y += kexec.o
> +endif
> +endif
> +
> obj-$(CONFIG_OF_UNITTEST) += unittest-data/
> diff --git a/drivers/of/kexec.c b/drivers/of/kexec.c
> new file mode 100644
> index 000000000000..469e09613cdd
> --- /dev/null
> +++ b/drivers/of/kexec.c
> @@ -0,0 +1,258 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2020 Arm Limited
> + *
> + * Based on arch/arm64/kernel/machine_kexec_file.c:
> + * Copyright (C) 2018 Linaro Limited
> + *
> + * And arch/powerpc/kexec/file_load.c:
> + * Copyright (C) 2016 IBM Corporation
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/kexec.h>
> +#include <linux/libfdt.h>
> +#include <linux/of.h>
> +#include <linux/of_fdt.h>
> +#include <linux/random.h>
> +#include <linux/types.h>
> +
> +/* relevant device tree properties */
> +#define FDT_PROP_KEXEC_ELFHDR "linux,elfcorehdr"
> +#define FDT_PROP_MEM_RANGE "linux,usable-memory-range"
> +#define FDT_PROP_INITRD_START "linux,initrd-start"
> +#define FDT_PROP_INITRD_END "linux,initrd-end"
> +#define FDT_PROP_BOOTARGS "bootargs"
> +#define FDT_PROP_KASLR_SEED "kaslr-seed"
> +#define FDT_PROP_RNG_SEED "rng-seed"
> +#define RNG_SEED_SIZE 128
> +
> +/**
> + * fdt_find_and_del_mem_rsv - delete memory reservation with given address and size
> + *
> + * @fdt: Flattened device tree for the current kernel.
> + * @start: Starting address of the reserved memory.
> + * @size: Size of the reserved memory.
> + *
> + * Return: 0 on success, or negative errno on error.
> + */
> +static int fdt_find_and_del_mem_rsv(void *fdt, unsigned long start, unsigned long size)
> +{
> + int i, ret, num_rsvs = fdt_num_mem_rsv(fdt);
> +
> + for (i = 0; i < num_rsvs; i++) {
> + u64 rsv_start, rsv_size;
> +
> + ret = fdt_get_mem_rsv(fdt, i, &rsv_start, &rsv_size);
> + if (ret) {
> + pr_err("Malformed device tree.\n");
> + return -EINVAL;
> + }
> +
> + if (rsv_start == start && rsv_size == size) {
> + ret = fdt_del_mem_rsv(fdt, i);
> + if (ret) {
> + pr_err("Error deleting device tree reservation.\n");
> + return -EINVAL;
> + }
> +
> + return 0;
> + }
> + }
> +
> + return -ENOENT;
> +}
> +
> +/*
> + * of_kexec_alloc_and_setup_fdt - Alloc and setup a new Flattened Device Tree
> + *
> + * @image: kexec image being loaded.
> + * @initrd_load_addr: Address where the next initrd will be loaded.
> + * @initrd_len: Size of the next initrd, or 0 if there will be none.
> + * @cmdline: Command line for the next kernel, or NULL if there will
> + * be none.
> + *
> + * Return: fdt on success, or NULL errno on error.
> + */
> +void *of_kexec_alloc_and_setup_fdt(const struct kimage *image,
> + unsigned long initrd_load_addr,
> + unsigned long initrd_len,
> + const char *cmdline)
> +{
> + void *fdt;
> + int ret, chosen_node;
> + const void *prop;
> + unsigned long fdt_size;
> +
> + fdt_size = fdt_totalsize(initial_boot_params) +
> + (cmdline ? strlen(cmdline) : 0) +
> + FDT_EXTRA_SPACE;

Just adding 4 KB to initial_boot_params won't be enough for crash
kernels on ppc64. The current powerpc code doubles the size of
initial_boot_params (which is normally larger than 4 KB) and even that
isn't enough. A patch was added to powerpc/next today which uses a more
precise (but arch-specific) formula:

https://lore.kernel.org/linuxppc-dev/161243826811.119001.14083048209224609814.stgit@hbathini/

So I believe we need a hook here where architectures can provide their
own specific calculation for the size of the fdt. Perhaps a weakly
defined function providing a default implementation which an
arch-specific file can override (a la arch_kexec_kernel_image_load())?

Then the powerpc specific hook would be the kexec_fdt_totalsize_ppc64()
function from the patch I linked above.

--
Thiago Jung Bauermann
IBM Linux Technology Center