linux-kernel - Re: [PATCH v22 4/9] arm64: kdump: Don't force page-level mappings for memory above 4G

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Message-ID: <b635e4e8-a05d-36e5-9274-885452fd0a06@huawei.com>
Date:   Wed, 27 Apr 2022 15:12:29 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Catalin Marinas <catalin.marinas@....com>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        <x86@...nel.org>, "H . Peter Anvin" <hpa@...or.com>,
        <linux-kernel@...r.kernel.org>, Dave Young <dyoung@...hat.com>,
        Baoquan He <bhe@...hat.com>, Vivek Goyal <vgoyal@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        <kexec@...ts.infradead.org>, Will Deacon <will@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        <devicetree@...r.kernel.org>, "Jonathan Corbet" <corbet@....net>,
        <linux-doc@...r.kernel.org>, Randy Dunlap <rdunlap@...radead.org>,
        Feng Zhou <zhoufeng.zf@...edance.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Chen Zhou <dingguo.cz@...group.com>,
        "John Donnelly" <John.p.donnelly@...cle.com>,
        Dave Kleikamp <dave.kleikamp@...cle.com>
Subject: Re: [PATCH v22 4/9] arm64: kdump: Don't force page-level mappings for
 memory above 4G



On 2022/4/26 22:26, Catalin Marinas wrote:
> On Thu, Apr 14, 2022 at 07:57:15PM +0800, Zhen Lei wrote:
>> @@ -540,13 +540,31 @@ static void __init map_mem(pgd_t *pgdp)
>>  	for_each_mem_range(i, &start, &end) {
>>  		if (start >= end)
>>  			break;
>> +
>> +#ifdef CONFIG_KEXEC_CORE
>> +		if (eflags && (end >= SZ_4G)) {
>> +			/*
>> +			 * The memory block cross the 4G boundary.
>> +			 * Forcibly use page-level mappings for memory under 4G.
>> +			 */
>> +			if (start < SZ_4G) {
>> +				__map_memblock(pgdp, start, SZ_4G - 1,
>> +					       pgprot_tagged(PAGE_KERNEL), flags | eflags);
>> +				start  = SZ_4G;
>> +			}
>> +
>> +			/* Page-level mappings is not mandatory for memory above 4G */
>> +			eflags = 0;
>> +		}
>> +#endif
> 
> That's a bit tricky if a SoC has all RAM above 4G. IIRC AMD Seattle had
> this layout. See max_zone_phys() for how we deal with this, basically
> extending ZONE_DMA to the whole range if RAM starts above 4GB. In that
> case, crashkernel reservation would fall in the range above 4GB.
> 
> BTW, we changed the max_zone_phys() logic with commit 791ab8b2e3db
> ("arm64: Ignore any DMA offsets in the max_zone_phys() calculation").

Okay, thanks for your correction. I'll dig into it after I've done the original requirement.

> 

-- 
Regards,
  Zhen Lei