Re: [PATCH 06/15] arm64: Add KHO support

[Rob Herring <robh@kernel.org>]

On Wed, Dec 13, 2023 at 12:04:43AM +0000, Alexander Graf wrote:
> We now have all bits in place to support KHO kexecs. This patch adds
> awareness of KHO in the kexec file as well as boot path for arm64 and
> adds the respective kconfig option to the architecture so that it can
> use KHO successfully.
> 
> Signed-off-by: Alexander Graf <graf@amazon.com>
> ---
>  arch/arm64/Kconfig        | 12 ++++++++++++
>  arch/arm64/kernel/setup.c |  2 ++
>  arch/arm64/mm/init.c      |  8 ++++++++
>  drivers/of/fdt.c          | 41 +++++++++++++++++++++++++++++++++++++++
>  drivers/of/kexec.c        | 36 ++++++++++++++++++++++++++++++++++
>  5 files changed, 99 insertions(+)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 7b071a00425d..1ba338ce7598 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1501,6 +1501,18 @@ config ARCH_SUPPORTS_CRASH_DUMP
>  config ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION
>  	def_bool CRASH_CORE
>  
> +config KEXEC_KHO
> +	bool "kexec handover"
> +	depends on KEXEC
> +	select MEMBLOCK_SCRATCH
> +	select LIBFDT
> +	select CMA
> +	help
> +	  Allow kexec to hand over state across kernels by generating and
> +	  passing additional metadata to the target kernel. This is useful
> +	  to keep data or state alive across the kexec. For this to work,
> +	  both source and target kernels need to have this option enabled.

Why do we have the same kconfig entry twice? Here and x86.

> +
>  config TRANS_TABLE
>  	def_bool y
>  	depends on HIBERNATION || KEXEC_CORE
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> index 417a8a86b2db..8035b673d96d 100644
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -346,6 +346,8 @@ void __init __no_sanitize_address setup_arch(char **cmdline_p)
>  
>  	paging_init();
>  
> +	kho_reserve_mem();
> +
>  	acpi_table_upgrade();
>  
>  	/* Parse the ACPI tables for possible boot-time configuration */
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 74c1db8ce271..254d82f3383a 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -358,6 +358,8 @@ void __init bootmem_init(void)
>  	 */
>  	arch_reserve_crashkernel();
>  
> +	kho_reserve();
> +

reserve what? It is not obvious what the difference between 
kho_reserve_mem() and kho_reserve() are.

>  	memblock_dump_all();
>  }
>  
> @@ -386,6 +388,12 @@ void __init mem_init(void)
>  	/* this will put all unused low memory onto the freelists */
>  	memblock_free_all();
>  
> +	/*
> +	 * Now that all KHO pages are marked as reserved, let's flip them back
> +	 * to normal pages with accurate refcount.
> +	 */
> +	kho_populate_refcount();
> +
>  	/*
>  	 * Check boundaries twice: Some fundamental inconsistencies can be
>  	 * detected at build time already.
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index bf502ba8da95..af95139351ed 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -1006,6 +1006,44 @@ void __init early_init_dt_check_for_usable_mem_range(void)
>  		memblock_add(rgn[i].base, rgn[i].size);
>  }
>  
> +/**
> + * early_init_dt_check_kho - Decode info required for kexec handover from DT
> + */
> +void __init early_init_dt_check_kho(void)
> +{
> +#ifdef CONFIG_KEXEC_KHO

if (!IS_ENABLED(CONFIG_KEXEC_KHO))
  return;

You'll need a kho_populate() stub.

> +	unsigned long node = chosen_node_offset;
> +	u64 kho_start, scratch_start, scratch_size, mem_start, mem_size;
> +	const __be32 *p;
> +	int l;
> +
> +	if ((long)node < 0)
> +		return;
> +
> +	p = of_get_flat_dt_prop(node, "linux,kho-dt", &l);
> +	if (l != (dt_root_addr_cells + dt_root_size_cells) * sizeof(__be32))
> +		return;
> +
> +	kho_start = dt_mem_next_cell(dt_root_addr_cells, &p);
> +
> +	p = of_get_flat_dt_prop(node, "linux,kho-scratch", &l);
> +	if (l != (dt_root_addr_cells + dt_root_size_cells) * sizeof(__be32))
> +		return;
> +
> +	scratch_start = dt_mem_next_cell(dt_root_addr_cells, &p);
> +	scratch_size = dt_mem_next_cell(dt_root_addr_cells, &p);
> +
> +	p = of_get_flat_dt_prop(node, "linux,kho-mem", &l);
> +	if (l != (dt_root_addr_cells + dt_root_size_cells) * sizeof(__be32))
> +		return;
> +
> +	mem_start = dt_mem_next_cell(dt_root_addr_cells, &p);
> +	mem_size = dt_mem_next_cell(dt_root_addr_cells, &p);
> +
> +	kho_populate(kho_start, scratch_start, scratch_size, mem_start, mem_size);
> +#endif
> +}
> +
>  #ifdef CONFIG_SERIAL_EARLYCON
>  
>  int __init early_init_dt_scan_chosen_stdout(void)
> @@ -1304,6 +1342,9 @@ void __init early_init_dt_scan_nodes(void)
>  
>  	/* Handle linux,usable-memory-range property */
>  	early_init_dt_check_for_usable_mem_range();
> +
> +	/* Handle kexec handover */
> +	early_init_dt_check_kho();
>  }
>  
>  bool __init early_init_dt_scan(void *params)
> diff --git a/drivers/of/kexec.c b/drivers/of/kexec.c
> index 68278340cecf..a612e6bb8c75 100644
> --- a/drivers/of/kexec.c
> +++ b/drivers/of/kexec.c
> @@ -264,6 +264,37 @@ static inline int setup_ima_buffer(const struct kimage *image, void *fdt,
>  }
>  #endif /* CONFIG_IMA_KEXEC */
>  
> +static int kho_add_chosen(const struct kimage *image, void *fdt, int chosen_node)
> +{
> +	int ret = 0;
> +
> +#ifdef CONFIG_KEXEC_KHO

ditto

Though perhaps image->kho is not defined?


> +	if (!image->kho.dt.buffer || !image->kho.mem_cache.buffer)
> +		goto out;
> +
> +	pr_debug("Adding kho metadata to DT");
> +
> +	ret = fdt_appendprop_addrrange(fdt, 0, chosen_node, "linux,kho-dt",
> +				       image->kho.dt.mem, image->kho.dt.memsz);
> +	if (ret)
> +		goto out;
> +
> +	ret = fdt_appendprop_addrrange(fdt, 0, chosen_node, "linux,kho-scratch",
> +				       kho_scratch_phys, kho_scratch_len);
> +	if (ret)
> +		goto out;
> +
> +	ret = fdt_appendprop_addrrange(fdt, 0, chosen_node, "linux,kho-mem",
> +				       image->kho.mem_cache.mem,
> +				       image->kho.mem_cache.bufsz);
> +	if (ret)
> +		goto out;
> +
> +out:
> +#endif
> +	return ret;
> +}
> +
>  /*
>   * of_kexec_alloc_and_setup_fdt - Alloc and setup a new Flattened Device Tree
>   *
> @@ -412,6 +443,11 @@ void *of_kexec_alloc_and_setup_fdt(const struct kimage *image,
>  		}
>  	}
>  
> +	/* Add kho metadata if this is a KHO image */
> +	ret = kho_add_chosen(image, fdt, chosen_node);
> +	if (ret)
> +		goto out;
> +
>  	/* add bootargs */
>  	if (cmdline) {
>  		ret = fdt_setprop_string(fdt, chosen_node, "bootargs", cmdline);
> -- 
> 2.40.1
> 
> 
> 
> 
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