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Date:   Sun, 4 Jun 2023 11:50:44 +0800
From:   Baoquan He <bhe@redhat.com>
To:     Chen Jiahao <chenjiahao16@huawei.com>
Cc:     linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
        kexec@lists.infradead.org, linux-doc@vger.kernel.org,
        paul.walmsley@sifive.com, palmer@dabbelt.com,
        conor.dooley@microchip.com, guoren@kernel.org, heiko@sntech.de,
        bjorn@rivosinc.com, alex@ghiti.fr, akpm@linux-foundation.org,
        atishp@rivosinc.com, thunder.leizhen@huawei.com, horms@kernel.org
Subject: Re: [PATCH -next v5 1/2] riscv: kdump: Implement
 crashkernel=X,[high,low]
Message-ID: <ZHwKFADVXyNYJBCp@MiWiFi-R3L-srv>
References: <20230511085139.1039088-1-chenjiahao16@huawei.com>
 <20230511085139.1039088-2-chenjiahao16@huawei.com>
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In-Reply-To: <20230511085139.1039088-2-chenjiahao16@huawei.com>
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Hi Jiahao,

On 05/11/23 at 04:51pm, Chen Jiahao wrote:
......  
> @@ -1300,14 +1325,34 @@ static void __init reserve_crashkernel(void)
>  		return;
>  	}
>  
> -	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
> +	ret = parse_crashkernel(cmdline, memblock_phys_mem_size(),
>  				&crash_size, &crash_base);
> -	if (ret || !crash_size)
> +	if (ret == -ENOENT) {
> +		/* Fallback to crashkernel=X,[high,low] */
> +		ret = parse_crashkernel_high(cmdline, 0, &crash_size, &crash_base);
> +		if (ret || !crash_size)
> +			return;
> +
> +		/*
> +		 * crashkernel=Y,low is valid only when crashkernel=X,high
> +		 * is passed.
> +		 */
> +		ret = parse_crashkernel_low(cmdline, 0, &crash_low_size, &crash_base);
> +		if (ret == -ENOENT)
> +			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> +		else if (ret)
> +			return;
> +
> +		search_end = memblock_end_of_DRAM();
> +	} else if (ret || !crash_size) {
> +		/* Invalid argument value specified */
>  		return;
> +	}

The parsing part looks great, while you didn't mark if it's specified
high reservation, please see later comment why it's needed.

>  
>  	crash_size = PAGE_ALIGN(crash_size);
>  
>  	if (crash_base) {
> +		fixed_base = true;
>  		search_start = crash_base;
>  		search_end = crash_base + crash_size;
>  	}
> @@ -1320,17 +1365,31 @@ static void __init reserve_crashkernel(void)
>  	 * swiotlb can work on the crash kernel.
>  	 */
>  	crash_base = memblock_phys_alloc_range(crash_size, PMD_SIZE,
> -					       search_start,
> -					       min(search_end, (unsigned long) SZ_4G));
> +					       search_start, search_end);

If it's a specified high reservation, you have 
search_start = memblock_start_of_DRAM();
search_end = memblock_end_of_DRAM();

Then it attempts to search top down first time here.

>  	if (crash_base == 0) {
> -		/* Try again without restricting region to 32bit addressible memory */
> +		if (fixed_base) {
> +			pr_warn("crashkernel: allocating failed with given size@offset\n");
> +			return;
> +		}
> +		search_end = memblock_end_of_DRAM();
> +
> +		/* Try again above the region of 32bit addressible memory */
>  		crash_base = memblock_phys_alloc_range(crash_size, PMD_SIZE,
> -						search_start, search_end);
> +						       search_start, search_end);

If crashkernel=,high case, the first attempt failed, here it assigns
search_end with memblock_end_of_DRAM(). It's the exactly the same
attempt, why is that needed? Why don't you use a local variable 'high'
to mark the crashkernel=,hig, then judge when deciding how to adjsut the
reservation range.

Do I misunderstand the code? 

Thanks
Baoquan

>  		if (crash_base == 0) {
>  			pr_warn("crashkernel: couldn't allocate %lldKB\n",
>  				crash_size >> 10);
>  			return;
>  		}
> +
> +		if (!crash_low_size)
> +			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> +	}
> +
> +	if ((crash_base > dma32_phys_limit - crash_low_size) &&
> +	    crash_low_size && reserve_crashkernel_low(crash_low_size)) {
> +		memblock_phys_free(crash_base, crash_size);
> +		return;
>  	}
>  
>  	pr_info("crashkernel: reserved 0x%016llx - 0x%016llx (%lld MB)\n",
> -- 
> 2.31.1
>