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From:   Thiago Jung Bauermann <bauerman@linux.ibm.com>
To:     Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Cc:     zohar@linux.ibm.com, robh@kernel.org, takahiro.akashi@linaro.org,
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Subject: Re: [PATCH v17 02/10] of: Add a common kexec FDT setup function
In-reply-to: <20210209182200.30606-3-nramas@linux.microsoft.com>
Date:   Thu, 11 Feb 2021 22:09:18 -0300
Message-ID: <87k0reozwh.fsf@manicouagan.localdomain>
MIME-Version: 1.0
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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