linux-kernel - Re: [PATCH v2 resend 2/3] arm64: mm: Don't defer reserve_crashkernel() with dma_force

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Message-ID: <73e5583d-2f32-8837-e32a-93f127f0a40b@huawei.com>
Date:   Mon, 11 Apr 2022 16:28:14 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Vijay Balakrishna <vijayb@...ux.microsoft.com>,
        <catalin.marinas@....com>, <will@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
CC:     <f.fainelli@...il.com>
Subject: Re: [PATCH v2 resend 2/3] arm64: mm: Don't defer
 reserve_crashkernel() with dma_force_32bit


On 2022/4/2 6:09, Vijay Balakrishna wrote:
>
>
> On 3/31/2022 12:40 AM, Kefeng Wang wrote:
>> ARM64 enable ZONE_DMA by default, and with ZONE_DMA crash kernel
>> memory reservation is delayed until DMA zone memory range size
>> initilazation performed in zone_sizes_init(), but for most platforms
>> use 32bit dma_zone_bits, so add dma_force_32bit kernel parameter
>> if ZONE_DMA enabled, and initialize arm64_dma_phys_limit to
>> dma32_phys_limit in arm64_memblock_init() if dma_force_32bit
>> is setup, this could let the crash kernel reservation earlier,
>> and allows linear creation with block mapping.
>>
>> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
>
> I don't see any problem with the approach.  Hope you or someone can 
> test to make sure no surprises on RPi4 with the proposed change.  I do 
> understand on RPi4 --
>
> - both ZONE_DMA and ZONE_DMA32 are enabled
> - one wouldn't use dma_force_32bit kernel parameter
> - crashkernel_could_early_reserve() would return false to preserve 
> late reserve of crash kernel memory
>
I don't have RPi4, I tested following cases on qemu

1) only with ZONE_DMA

     1.1) only with ZONE_DMA and with dma_force_32bit

2) only with ZONE_DMA32

3) with ZONE_DMA and ZONE_DMA32

    3.1) with ZONE_DMA and ZONE_DMA32 and with dma_force_32bit

> nit --
> - consider renaming crashkernel_could_early_reserve() => 
> crashkernel_early_reserve()
>
Sure.
> Reviewed-by: Vijay Balakrishna <vijayb@...ux.microsoft.com>
>
Thanks.