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

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Message-ID: <b14ac6d4-9d29-4193-ac2f-7e7d7ae3a60a@gmail.com>
Date: Mon, 7 Oct 2024 14:54:07 +0100
From: Usama Arif <usamaarif642@...il.com>
To: Saravana Kannan <saravanak@...gle.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 03/10/2024 21:20, Saravana Kannan wrote:
> 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
> 

Thanks, will do in the next revision.