linux-kernel - Re: [PATCH v4 0/3] arm64: support page mapping percpu first chunk allocator

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Date:   Mon, 11 Oct 2021 09:09:29 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     <will@...nel.org>, <catalin.marinas@....com>,
        <ryabinin.a.a@...il.com>, <andreyknvl@...il.com>,
        <dvyukov@...gle.com>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <elver@...gle.com>, <gregkh@...uxfoundation.org>,
        <kasan-dev@...glegroups.com>
Subject: Re: [PATCH v4 0/3] arm64: support page mapping percpu first chunk
 allocator



On 2021/10/11 5:36, Andrew Morton wrote:
> On Fri, 10 Sep 2021 13:33:51 +0800 Kefeng Wang <wangkefeng.wang@...wei.com> wrote:
> 
>> Percpu embedded first chunk allocator is the firstly option, but it
>> could fails on ARM64, eg,
>>    "percpu: max_distance=0x5fcfdc640000 too large for vmalloc space 0x781fefff0000"
>>    "percpu: max_distance=0x600000540000 too large for vmalloc space 0x7dffb7ff0000"
>>    "percpu: max_distance=0x5fff9adb0000 too large for vmalloc space 0x5dffb7ff0000"
>>
>> then we could meet "WARNING: CPU: 15 PID: 461 at vmalloc.c:3087 pcpu_get_vm_areas+0x488/0x838",
>> even the system could not boot successfully.
>>
>> Let's implement page mapping percpu first chunk allocator as a fallback
>> to the embedding allocator to increase the robustness of the system.
>>
>> Also fix a crash when both NEED_PER_CPU_PAGE_FIRST_CHUNK and KASAN_VMALLOC enabled.
> 
> How serious are these problems in real-world situations?  Do people
> feel that a -stable backport is needed, or is a 5.16-rc1 merge
> sufficient?
> .
Thanks Andrew.

A specific memory layout is required(also with KASAN enabled), we met 
this issue at qemu and real hardware, due to KASAN enabled, so I think
5.16-rc1 is sufficient.