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Subject: Re: [PATCH 2/3] arm64: kdump: do not map crashkernel region
 specifically
To:     Baoquan He <bhe@redhat.com>, <linux-kernel@vger.kernel.org>
CC:     <catalin.marinas@arm.com>, <horms@kernel.org>,
        <John.p.donnelly@oracle.com>, <will@kernel.org>,
        <kexec@lists.infradead.org>, <ardb@kernel.org>, <rppt@kernel.org>,
        <linux-arm-kernel@lists.infradead.org>
References: <20230324131838.409996-1-bhe@redhat.com>
 <20230324131838.409996-3-bhe@redhat.com>
From:   "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
Message-ID: <36566d76-2e15-75c2-6c3b-2784aa8d2332@huawei.com>
Date:   Sat, 25 Mar 2023 09:57:40 +0800
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On 2023/3/24 21:18, Baoquan He wrote:
> After taking off the protection functions on crashkernel memory region,
> there's no need to map crashkernel region with page granularity during
> linear mapping.
> 
> With this change, the system can make use of block or section mapping
> on linear region to largely improve perforcemence during system bootup
> and running.
> 
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
>  arch/arm64/mm/mmu.c | 43 -------------------------------------------
>  1 file changed, 43 deletions(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 6f9d8898a025..7556020a27b7 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -510,21 +510,6 @@ void __init mark_linear_text_alias_ro(void)
>  			    PAGE_KERNEL_RO);
>  }
>  
> -static bool crash_mem_map __initdata;
> -
> -static int __init enable_crash_mem_map(char *arg)
> -{
> -	/*
> -	 * Proper parameter parsing is done by reserve_crashkernel(). We only
> -	 * need to know if the linear map has to avoid block mappings so that
> -	 * the crashkernel reservations can be unmapped later.
> -	 */
> -	crash_mem_map = true;
> -
> -	return 0;
> -}
> -early_param("crashkernel", enable_crash_mem_map);
> -
>  static void __init map_mem(pgd_t *pgdp)
>  {
>  	static const u64 direct_map_end = _PAGE_END(VA_BITS_MIN);
> @@ -554,16 +539,6 @@ static void __init map_mem(pgd_t *pgdp)
>  	 */
>  	memblock_mark_nomap(kernel_start, kernel_end - kernel_start);
>  
> -#ifdef CONFIG_KEXEC_CORE
> -	if (crash_mem_map) {
> -		if (defer_reserve_crashkernel())
> -			flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
> -		else if (crashk_res.end)
> -			memblock_mark_nomap(crashk_res.start,
> -			    resource_size(&crashk_res));
> -	}
> -#endif
> -
>  	/* map all the memory banks */
>  	for_each_mem_range(i, &start, &end) {
>  		if (start >= end)
> @@ -590,24 +565,6 @@ static void __init map_mem(pgd_t *pgdp)
>  	__map_memblock(pgdp, kernel_start, kernel_end,
>  		       PAGE_KERNEL, NO_CONT_MAPPINGS);
>  	memblock_clear_nomap(kernel_start, kernel_end - kernel_start);
> -
> -	/*
> -	 * Use page-level mappings here so that we can shrink the region
> -	 * in page granularity and put back unused memory to buddy system
> -	 * through /sys/kernel/kexec_crash_size interface.
> -	 */
> -#ifdef CONFIG_KEXEC_CORE
> -	if (crash_mem_map && !defer_reserve_crashkernel()) {
> -		if (crashk_res.end) {
> -			__map_memblock(pgdp, crashk_res.start,
> -				       crashk_res.end + 1,
> -				       PAGE_KERNEL,
> -				       NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS);
> -			memblock_clear_nomap(crashk_res.start,
> -					     resource_size(&crashk_res));
> -		}
> -	}
> -#endif
>  }
>  
>  void mark_rodata_ro(void)
> 

Reviewed-by: Zhen Lei <thunder.leizhen@huawei.com>

-- 
Regards,
  Zhen Lei