linux-kernel - Re: [PATCH] of/kexec: save pa of initial_boot

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Message-ID: <CAGETcx9r+VwMBt=Ra-+-ZFgO66DK1LGjbT8cXFZ7v-c-N20qTQ@mail.gmail.com>
Date: Thu, 3 Oct 2024 13:20:10 -0700
From: Saravana Kannan <saravanak@...gle.com>
To: Usama Arif <usamaarif642@...il.com>
Cc: mark.rutland@....com, will@...nel.org, leitao@...ian.org, 
	catalin.marinas@....com, robh@...nel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	devicetree@...r.kernel.org, kexec@...ts.infradead.org
Subject: Re: [PATCH] of/kexec: save pa of initial_boot_params for arm64 and
 use it at kexec

On Thu, Oct 3, 2024 at 4:38 AM Usama Arif <usamaarif642@...il.com> wrote:
>
>  __pa() is only intended to be used for linear map addresses and using
> it for initial_boot_params which is in fixmap for arm64 will give an
> incorrect value. Hence stash the physical address when it is known at
> boot time and use it at kexec time instead of converting the virtual
> address using __pa().
>
> Reported-by: Breno Leitao <leitao@...ian.org>
> Suggested-by: Mark Rutland <mark.rutland@....com>
> Signed-off-by: Usama Arif <usamaarif642@...il.com>
> Fixes: ac10be5cdbfa ("arm64: Use common of_kexec_alloc_and_setup_fdt()")
> ---
>  arch/arm64/kernel/setup.c | 8 ++++++++
>  drivers/of/fdt.c          | 6 ++++++
>  drivers/of/kexec.c        | 8 ++++++--
>  include/linux/of_fdt.h    | 2 ++
>  4 files changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> index b22d28ec8028..a4d96f5e2e05 100644
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -194,6 +194,14 @@ static void __init setup_machine_fdt(phys_addr_t dt_phys)
>         /* Early fixups are done, map the FDT as read-only now */
>         fixmap_remap_fdt(dt_phys, &size, PAGE_KERNEL_RO);
>
> +       /*
> +        * Save dt_phys address so that it can be used later for kexec. This
> +        * is done as __pa() is only intended to be used for linear map addresses
> +        * and using it for initial_boot_params which is in fixmap will give an
> +        * incorrect value.
> +        */
> +       set_initial_boot_params_pa(dt_phys);
> +
>         name = of_flat_dt_get_machine_name();
>         if (!name)
>                 return;
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index 4d528c10df3a..9e312b7c246e 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -457,6 +457,7 @@ int __initdata dt_root_addr_cells;
>  int __initdata dt_root_size_cells;
>
>  void *initial_boot_params __ro_after_init;
> +phys_addr_t initial_boot_params_pa __ro_after_init;
>
>  #ifdef CONFIG_OF_EARLY_FLATTREE
>
> @@ -1185,6 +1186,11 @@ bool __init early_init_dt_scan(void *params)
>         return true;
>  }
>
> +void __init set_initial_boot_params_pa(phys_addr_t params)
> +{
> +       initial_boot_params_pa = params;
> +}
> +
>  static void *__init copy_device_tree(void *fdt)
>  {
>         int size;
> diff --git a/drivers/of/kexec.c b/drivers/of/kexec.c
> index 9ccde2fd77cb..ca9f27b27f71 100644
> --- a/drivers/of/kexec.c
> +++ b/drivers/of/kexec.c
> @@ -300,8 +300,12 @@ void *of_kexec_alloc_and_setup_fdt(const struct kimage *image,
>                 goto out;
>         }
>
> -       /* Remove memory reservation for the current device tree. */
> -       ret = fdt_find_and_del_mem_rsv(fdt, __pa(initial_boot_params),
> +       /* Remove memory reservation for the current device tree.
> +        * For arm64, initial_boot_params is a fixmap address, hence __pa(),
> +        * can't be used to get the physical address.
> +        */
> +       ret = fdt_find_and_del_mem_rsv(fdt, IS_ENABLED(CONFIG_ARM64) ?
> +                                      initial_boot_params_pa : __pa(initial_boot_params),
>                                        fdt_totalsize(initial_boot_params));

Not sure about the correctness of the patch (not a kexec expert) but
no need to do all of this inside a function parameter. Just create a
variable and use it here.

-Saravana

>         if (ret == -EINVAL) {
>                 pr_err("Error removing memory reservation.\n");
> diff --git a/include/linux/of_fdt.h b/include/linux/of_fdt.h
> index d69ad5bb1eb1..dbd99bf21ac8 100644
> --- a/include/linux/of_fdt.h
> +++ b/include/linux/of_fdt.h
> @@ -31,6 +31,7 @@ extern void *of_fdt_unflatten_tree(const unsigned long *blob,
>  extern int __initdata dt_root_addr_cells;
>  extern int __initdata dt_root_size_cells;
>  extern void *initial_boot_params;
> +extern phys_addr_t initial_boot_params_pa;
>
>  extern char __dtb_start[];
>  extern char __dtb_end[];
> @@ -73,6 +74,7 @@ extern int early_init_dt_scan_root(void);
>  extern bool early_init_dt_scan(void *params);
>  extern bool early_init_dt_verify(void *params);
>  extern void early_init_dt_scan_nodes(void);
> +extern void set_initial_boot_params_pa(phys_addr_t params);
>
>  extern const char *of_flat_dt_get_machine_name(void);
>  extern const void *of_flat_dt_match_machine(const void *default_match,
> --
> 2.43.5
>