From: "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Baoquan He <bhe@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>, <x86@kernel.org>,
"H . Peter Anvin" <hpa@zytor.com>, <linux-kernel@vger.kernel.org>,
Dave Young <dyoung@redhat.com>, Vivek Goyal <vgoyal@redhat.com>,
Eric Biederman <ebiederm@xmission.com>,
<kexec@lists.infradead.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
<linux-arm-kernel@lists.infradead.org>,
Rob Herring <robh+dt@kernel.org>,
Frank Rowand <frowand.list@gmail.com>,
<devicetree@vger.kernel.org>, "Jonathan Corbet" <corbet@lwn.net>,
<linux-doc@vger.kernel.org>, Randy Dunlap <rdunlap@infradead.org>,
Feng Zhou <zhoufeng.zf@bytedance.com>,
Kefeng Wang <wangkefeng.wang@huawei.com>,
Chen Zhou <dingguo.cz@antgroup.com>
Subject: Re: [PATCH v17 03/10] x86: kdump: use macro CRASH_ADDR_LOW_MAX in functions reserve_crashkernel()
Date: Thu, 16 Dec 2021 20:23:31 +0800 [thread overview]
Message-ID: <20d765ff-59bb-7bb3-df06-9f02eada3cb0@huawei.com> (raw)
In-Reply-To: <35810a61-604e-9b90-2a7f-cfca6ae042ac@huawei.com>
On 2021/12/16 20:08, Leizhen (ThunderTown) wrote:
>
>
> On 2021/12/16 19:07, Borislav Petkov wrote:
>> On Thu, Dec 16, 2021 at 10:46:12AM +0800, Leizhen (ThunderTown) wrote:
>>> The original value (1ULL << 32) is inaccurate
>>
>> I keep asking *why*?
>>
>>> and it enlarged the CRASH_ADDR_LOW upper limit.
>>
>> $ git grep -E "CRASH_ADDR_LOW\W"
>> $
>>
>> I have no clue what you mean here.
>
> #ifdef CONFIG_X86_32
> # define CRASH_ADDR_LOW_MAX SZ_512M
> # define CRASH_ADDR_HIGH_MAX SZ_512M
> #endif
>
> if (!high)
> (1) crash_base = memblock_phys_alloc_range(crash_size,
> CRASH_ALIGN, CRASH_ALIGN,
> CRASH_ADDR_LOW_MAX);
> if (!crash_base)
> (2) crash_base = memblock_phys_alloc_range(crash_size,
> CRASH_ALIGN, CRASH_ALIGN,
> CRASH_ADDR_HIGH_MAX);
>
> - if (crash_base >= (1ULL << 32) && reserve_crashkernel_low())
> +(3) if (crash_base >= CRASH_ADDR_LOW_MAX && reserve_crashkernel_low())
>
> If the memory of 'crash_base' is successfully allocated at (1), because the last
> parameter CRASH_ADDR_LOW_MAX is the upper bound, so we can sure that
> "crash_base < CRASH_ADDR_LOW_MAX". So that, reserve_crashkernel_low() will not be
> invoked at (3). That's why I said (1ULL << 32) is inaccurate and enlarge the CRASH_ADDR_LOW
> upper limit.
>
> If the memory of 'crash_base' is successfully allocated at (2), you see,
> CRASH_ADDR_HIGH_MAX = CRASH_ADDR_LOW_MAX = SZ_512M, the same as (1). In fact,
> "crashkernel=high," may not be recommended on X86_32.
>
> Is it possible that (CRASH_ADDR_HIGH_MAX >= 4G) and (CRASH_ADDR_LOW_MAX < 4G)?
> In this case, the memory allocated at (2) maybe over 4G. But why shouldn't
> CRASH_ADDR_LOW_MAX be equal to 4G at this point?
We divide two memory areas: low memory area and high memory area. The doc told us:
at least 256MB memory should be reserved at low memory area. So that if
"crash_base >= CRASH_ADDR_LOW_MAX" is true at (3), that means we have not reserved
any memory at low memory area, so we should call reserve_crashkernel_low().
The low memory area is not equivalent to <=4G, I think. So replace (1ULL << 32) with
CRASH_ADDR_LOW_MAX is logically correct.
>
>
>>
>>> This is because when the memory is allocated from the low end, the
>>> address cannot exceed CRASH_ADDR_LOW_MAX, see "if (!high)" branch.
>>
>>> If
>>> the memory is allocated from the high end, 'crash_base' is greater than or
>>> equal to (1ULL << 32), and naturally, it is greater than CRASH_ADDR_LOW_MAX.
>>>
>>> I think I should update the description, thanks.
>>
>> I think you should explain why is (1ULL << 32) wrong.
>>
>> It came from:
>>
>> eb6db83d1059 ("x86/setup: Do not reserve crashkernel high memory if low reservation failed")
>>
>> which simply frees the high memory portion when the low reservation
>> fails. And the test for that is, is crash base > 4G. So that makes
>> perfect sense to me.
>>
>> So your change is a NOP on 64-bit and it is a NOP on 32-bit by virtue of
>> the _low() variant always returning 0 on 32-bit.
>>
next prev parent reply other threads:[~2021-12-16 12:23 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-10 6:55 [PATCH v17 00/10] support reserving crashkernel above 4G on arm64 kdump Zhen Lei
2021-12-10 6:55 ` [PATCH v17 01/10] x86: kdump: replace the hard-coded alignment with macro CRASH_ALIGN Zhen Lei
2021-12-13 13:17 ` Baoquan He
2021-12-14 8:41 ` Leizhen (ThunderTown)
2021-12-13 14:26 ` john.p.donnelly
2021-12-13 19:54 ` Borislav Petkov
2021-12-14 9:27 ` Leizhen (ThunderTown)
2021-12-10 6:55 ` [PATCH v17 02/10] x86: kdump: make the lower bound of crash kernel reservation consistent Zhen Lei
2021-12-13 13:37 ` Baoquan He
2021-12-14 8:48 ` Leizhen (ThunderTown)
2021-12-13 14:27 ` john.p.donnelly
2021-12-14 19:07 ` Borislav Petkov
2021-12-14 19:24 ` Catalin Marinas
2021-12-15 2:10 ` Leizhen (ThunderTown)
2021-12-15 3:42 ` Baoquan He
2021-12-15 11:01 ` Catalin Marinas
2021-12-15 11:16 ` Baoquan He
2021-12-15 11:45 ` Leizhen (ThunderTown)
2021-12-10 6:55 ` [PATCH v17 03/10] x86: kdump: use macro CRASH_ADDR_LOW_MAX in functions reserve_crashkernel() Zhen Lei
2021-12-13 14:28 ` john.p.donnelly
2021-12-14 8:54 ` Baoquan He
2021-12-14 9:38 ` Borislav Petkov
2021-12-14 9:56 ` Baoquan He
2021-12-14 14:24 ` Borislav Petkov
2021-12-15 6:01 ` Baoquan He
2021-12-15 13:28 ` Borislav Petkov
2021-12-16 1:10 ` Baoquan He
2021-12-16 2:46 ` Leizhen (ThunderTown)
2021-12-16 11:07 ` Borislav Petkov
2021-12-16 12:08 ` Leizhen (ThunderTown)
2021-12-16 12:23 ` Leizhen (ThunderTown) [this message]
2021-12-16 14:48 ` Borislav Petkov
2021-12-17 2:51 ` Leizhen (ThunderTown)
2021-12-21 22:23 ` Borislav Petkov
2021-12-16 10:55 ` Borislav Petkov
2021-12-16 14:11 ` Baoquan He
2021-12-16 14:58 ` Borislav Petkov
2021-12-10 6:55 ` [PATCH v17 04/10] x86: kdump: move xen_pv_domain() check and insert_resource() to setup_arch() Zhen Lei
2021-12-13 14:29 ` john.p.donnelly
2021-12-14 11:40 ` Leizhen (ThunderTown)
2021-12-15 8:56 ` Leizhen (ThunderTown)
2021-12-15 9:22 ` Baoquan He
2021-12-10 6:55 ` [PATCH v17 05/10] x86: kdump: move reserve_crashkernel[_low]() into crash_core.c Zhen Lei
2021-12-13 14:30 ` john.p.donnelly
2021-12-14 10:45 ` Baoquan He
2021-12-14 12:38 ` Leizhen (ThunderTown)
2021-12-16 11:17 ` Borislav Petkov
2021-12-16 13:15 ` Leizhen (ThunderTown)
2021-12-16 14:51 ` Borislav Petkov
2021-12-10 6:55 ` [PATCH v17 06/10] arm64: kdump: introduce some macros for crash kernel reservation Zhen Lei
2021-12-13 14:30 ` john.p.donnelly
2021-12-10 6:55 ` [PATCH v17 07/10] arm64: kdump: reimplement crashkernel=X Zhen Lei
2021-12-13 14:31 ` john.p.donnelly
2021-12-10 6:55 ` [PATCH v17 08/10] of: fdt: Aggregate the processing of "linux,usable-memory-range" Zhen Lei
2021-12-10 16:39 ` Rob Herring
2021-12-13 14:34 ` john.p.donnelly
2021-12-10 6:55 ` [PATCH v17 09/10] of: fdt: Add memory for devices by DT property "linux,usable-memory-range" Zhen Lei
2021-12-10 16:43 ` Rob Herring
2021-12-13 14:33 ` john.p.donnelly
2021-12-10 6:55 ` [PATCH v17 10/10] kdump: update Documentation about crashkernel Zhen Lei
2021-12-13 14:34 ` john.p.donnelly
2021-12-10 7:15 ` [PATCH v17 00/10] support reserving crashkernel above 4G on arm64 kdump Kefeng Wang
2021-12-13 18:50 ` Will Deacon
2021-12-13 14:37 ` john.p.donnelly
2021-12-13 18:56 ` Catalin Marinas
2021-12-13 18:57 ` Borislav Petkov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20d765ff-59bb-7bb3-df06-9f02eada3cb0@huawei.com \
--to=thunder.leizhen@huawei.com \
--cc=bhe@redhat.com \
--cc=bp@alien8.de \
--cc=catalin.marinas@arm.com \
--cc=corbet@lwn.net \
--cc=devicetree@vger.kernel.org \
--cc=dingguo.cz@antgroup.com \
--cc=dyoung@redhat.com \
--cc=ebiederm@xmission.com \
--cc=frowand.list@gmail.com \
--cc=hpa@zytor.com \
--cc=kexec@lists.infradead.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=rdunlap@infradead.org \
--cc=robh+dt@kernel.org \
--cc=tglx@linutronix.de \
--cc=vgoyal@redhat.com \
--cc=wangkefeng.wang@huawei.com \
--cc=will@kernel.org \
--cc=x86@kernel.org \
--cc=zhoufeng.zf@bytedance.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).