linux-kernel - Re: [PATCH -fixes 2/2] riscv: Do not set initial_boot_params to the linear address of the dtb

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Message-ID: <08c3a597-0950-9756-9665-c017942de81f@ghiti.fr>
Date:   Wed, 29 Mar 2023 10:09:13 +0200
From:   Alexandre Ghiti <alex@...ti.fr>
To:     Conor Dooley <conor.dooley@...rochip.com>,
        Alexandre Ghiti <alexghiti@...osinc.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>, linux-doc@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -fixes 2/2] riscv: Do not set initial_boot_params to the
 linear address of the dtb

On 3/27/23 13:16, Conor Dooley wrote:
> On Thu, Mar 23, 2023 at 05:33:47PM +0100, Alexandre Ghiti wrote:
>> Now that the dtb early mapping was moved in the fixmap region, we can
>> keep using this address since it is present in swapper_pg_dir, so remove
>> the dtb relocation which was wrong anyway since early_memremap is
>> restricted to 256K whereas the maximum fdt size is 2MB.
> I feel bad making this comment since only one of us is a native speaker,
> but for the future would you mind breaking up overly long sentences like
> the above? Say:
>
> 	Now that the dtb early mapping was moved in the fixmap region, we can
> 	keep using this address since it is present in swapper_pg_dir, and
> 	remove the dtb relocation.
> 	The relocation was wrong anyway since early_memremap() is restricted to
> 	256K whereas the maximum fdt size is 2MB.

Sure!

>> Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
>> ---
>>   arch/riscv/kernel/setup.c |  5 +----
>>   arch/riscv/mm/init.c      | 21 ++-------------------
>>   2 files changed, 3 insertions(+), 23 deletions(-)
>>
>> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
>> index 542eed85ad2c..a059b73f4ddb 100644
>> --- a/arch/riscv/kernel/setup.c
>> +++ b/arch/riscv/kernel/setup.c
>> @@ -278,10 +278,7 @@ void __init setup_arch(char **cmdline_p)
>>   #if IS_ENABLED(CONFIG_BUILTIN_DTB)
>>   	unflatten_and_copy_device_tree();
>>   #else
>> -	if (early_init_dt_verify(__va(XIP_FIXUP(dtb_early_pa))))
> btw, how come it is safe now to drop this? This feels like a separate
> change that should be its own commit, no?

It is safe because early_init_dt_verify is already called in parse_dtb 
and since the dtb address does not change anymore, no need to reset 
initial_boot_params. So I'll split this one, thanks.

>
> Cheers,
> Conor.
>
>> -		unflatten_device_tree();
>> -	else
>> -		pr_err("No DTB found in kernel mappings\n");
>> +	unflatten_device_tree();
>>   #endif
>>   	misc_mem_init();
>>   
>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>> index fb78d6bbabae..0f14f4a8d179 100644
>> --- a/arch/riscv/mm/init.c
>> +++ b/arch/riscv/mm/init.c
>> @@ -249,25 +249,8 @@ static void __init setup_bootmem(void)
>>   	 * early_init_fdt_reserve_self() since __pa() does
>>   	 * not work for DTB pointers that are fixmap addresses
>>   	 */
>> -	if (!IS_ENABLED(CONFIG_BUILTIN_DTB)) {
>> -		/*
>> -		 * In case the DTB is not located in a memory region we won't
>> -		 * be able to locate it later on via the linear mapping and
>> -		 * get a segfault when accessing it via __va(dtb_early_pa).
>> -		 * To avoid this situation copy DTB to a memory region.
>> -		 * Note that memblock_phys_alloc will also reserve DTB region.
>> -		 */
>> -		if (!memblock_is_memory(dtb_early_pa)) {
>> -			size_t fdt_size = fdt_totalsize(dtb_early_va);
>> -			phys_addr_t new_dtb_early_pa = memblock_phys_alloc(fdt_size, PAGE_SIZE);
>> -			void *new_dtb_early_va = early_memremap(new_dtb_early_pa, fdt_size);
>> -
>> -			memcpy(new_dtb_early_va, dtb_early_va, fdt_size);
>> -			early_memunmap(new_dtb_early_va, fdt_size);
>> -			_dtb_early_pa = new_dtb_early_pa;
>> -		} else
>> -			memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
>> -	}
>> +	if (!IS_ENABLED(CONFIG_BUILTIN_DTB))
>> +		memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
>>   
>>   	dma_contiguous_reserve(dma32_phys_limit);
>>   	if (IS_ENABLED(CONFIG_64BIT))
>> -- 
>> 2.37.2
>>
>>
>>
>> _______________________________________________
>> linux-riscv mailing list
>> linux-riscv@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-riscv

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