linux-kernel - Re: [PATCH 2/2] arm64: mm: fix kdump broken with ZONE

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Date:   Mon, 28 Dec 2020 15:32:35 +0800
From:   chenzhou <chenzhou10@...wei.com>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        <catalin.marinas@....com>, <will@...nel.org>
CC:     <ardb@...nel.org>, <akpm@...ux-foundation.org>, <rppt@...nel.org>,
        <song.bao.hua@...ilicon.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <huawei.libin@...wei.com>,
        <xiexiuqi@...wei.com>
Subject: Re: [PATCH 2/2] arm64: mm: fix kdump broken with ZONE_DMA
 reintroduced

Hi Nicolas,

Thanks for your review.


On 2020/12/26 18:34, Nicolas Saenz Julienne wrote:
> Hi Chen, thanks for looking at this.
>
> On Sat, 2020-12-26 at 11:35 +0800, Chen Zhou wrote:
>> If the memory reserved for crash dump kernel falled in ZONE_DMA32,
>> the devices in crash dump kernel need to use ZONE_DMA will alloc fail.
>>
>> Fix this by reserving low memory in ZONE_DMA if CONFIG_ZONE_DMA is
>> enabled, otherwise, reserving in ZONE_DMA32.
>>
>> Fixes: bff3b04460a8 ("arm64: mm: reserve CMA and crashkernel in ZONE_DMA32")
> I'm not so sure this counts as a fix, if someone backports it it'll probably
> break things as it depends on the series that dynamically sizes DMA zones.
I write this just because kdump is broken from this commit.
>
>> Signed-off-by: Chen Zhou <chenzhou10@...wei.com>
>> ---
> Why not doing the same with CMA? You'll probably have to move the
> dma_contiguous_reserve() call into bootmem_init() so as to make sure that
> arm64_dma_phys_limit is populated.
You are right, CMA also need this. I will do this in next version.

Thanks,
Chen Zhou
>
> Regards,
> Nicolas
>
>>  arch/arm64/mm/init.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 7b9809e39927..5074e945f1a6 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -85,7 +85,8 @@ static void __init reserve_crashkernel(void)
>>  
>>
>>  	if (crash_base == 0) {
>>  		/* Current arm64 boot protocol requires 2MB alignment */
>> -		crash_base = memblock_find_in_range(0, arm64_dma32_phys_limit,
>> +		crash_base = memblock_find_in_range(0,
>> +				arm64_dma_phys_limit ? : arm64_dma32_phys_limit,
>>  				crash_size, SZ_2M);
>>  		if (crash_base == 0) {
>>  			pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
>