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Date:   Mon, 25 Apr 2022 10:45:15 +0800
From:   Baoquan He <bhe@redhat.com>
To:     "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        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>,
        John Donnelly <John.p.donnelly@oracle.com>,
        Dave Kleikamp <dave.kleikamp@oracle.com>
Subject: Re: [PATCH v22 0/9] support reserving crashkernel above 4G on arm64
 kdump
Message-ID: <YmYLO58lH0rf1c8B@MiWiFi-R3L-srv>
References: <20220414115720.1887-1-thunder.leizhen@huawei.com>
 <9e3f69fb-ac2b-6de5-459c-5d104247a0ac@huawei.com>
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On 04/25/22 at 10:19am, Leizhen (ThunderTown) wrote:
> 
> Hi, Catalin Marinas and Will Deacon:
>   Do you have time to review patches 3-4 and 6-7? These patches are a little more
> relevant to the arm64 architecture.
> 
> Hi, Baoquan He:
>   Can you review patches 1 and 5 again?

Yes, and I will test and review the whole series if no one check the
arm64 related changes.

> 
> 
> On 2022/4/14 19:57, Zhen Lei wrote:
> > Changes since [v21]:
> > 1. Update the commit message of  patch 1 and 5.
> > 2. Add some comments for reserve_crashkernel() in patch 5.
> > 
> > Thanks to Baoquan He and John Donnelly for their review comments.
> > 
> > Because v5.18-rc1 has added a new patch
> > commit  031495635b46 ("arm64: Do not defer reserve_crashkernel() for platforms with no DMA memory zones")
> > There are many new scenarios:
> > 1) The mappings may be block or page-level. 
> > 2) The call to reserve_crashkernel() may or may not be deferred.
> > 3) The the upper limit of DMA address may be 4G, or less than 4G. Or the
> >    upper limit of physical memory, because SMMU can do the mapping.
> > 
> > The code of patch 1-2, 8-9 keep no change, because the above-mentioned issues are not involved.
> > The code of patch 5 only makes the following changes:
> > -	if (crash_base >= SZ_4G)
> > +	/*
> > +	 * When both CONFIG_ZONE_DMA and CONFIG_ZONE_DMA32 are disabled, the
> > +	 * CRASH_ADDR_LOW_MAX equals the upper limit of physical memory, so
> > +	 * the 'crash_base' of high memory can not exceed it. To follow the
> > +	 * description of "crashkernel=X,high" option, add below 'high'
> > +	 * condition to make sure the crash low memory will be reserved.
> > +	 */
> > +	if ((crash_base >= CRASH_ADDR_LOW_MAX) || high) {
> > Change SZ_4G to CRASH_ADDR_LOW_MAX, because arm64_dma_phys_limit may be less than
> > 4G or greater than 4G. The check 'high' is used for "crashkernel=X,high" and
> > "(crash_base >= CRASH_ADDR_LOW_MAX)" is used for "crashkernel=X[@offset]".
> > 
> > Patch 3-4 to allow block mappings for memory above 4G.
> > Patch 6-7 to support only crash high memory or fixed memory range specified by
> > crashkernel=X@offset use page-level mapping, to allow other areas use block mapping.
> > These four patches are for performance optimization purposes. For details about the
> > technical feasibility analysis, please see the commit messages.
> > 
> > Now the implementation of arm64 is very different from that of x86. It's no longer
> > suitable for both of them to share code.
> > 
> > 
> > 
> > Changes since [v20]:
> > 1. Check whether crashkernel=Y,low is incorrectly configured or not configured. Do different processing.
> > 2. Share the existing description of x86. The configuration of arm64 is the same as that of x86.
> > 3. Define the value of macro CRASH_ADDR_HIGH_MAX as memblock.current_limit, instead of MEMBLOCK_ALLOC_ACCESSIBLE.
> > 4. To improve readability, some lightweight code adjustments have been made to reserve_craskernel(), including comments.
> > 5. The defined value of DEFAULT_CRASH_KERNEL_LOW_SIZE reconsiders swiotlb, just like x86, to share documents.
> > 
> > Thanks to Baoquan He for his careful review.
> > 
> > The test cases are as follows: (Please update the kexec tool to the latest version)
> > 1) crashkernel=4G						//high=4G, low=256M
> > 2) crashkernel=4G crashkernel=512M,high crashkernel=512M,low	//high=4G, low=256M, high and low are ignored
> > 3) crashkernel=4G crashkernel=512M,high				//high=4G, low=256M, high is ignored
> > 4) crashkernel=4G crashkernel=512M,low				//high=4G, low=256M, low is ignored
> > 5) crashkernel=4G@0xe0000000					//high=0G, low=0M, cannot allocate, failed
> > 6) crashkernel=512M						//high=0G, low=512M
> > 7) crashkernel=128M						//high=0G, low=128M
> > 8) crashkernel=512M@0xde000000		//512M@3552M		//high=0G, low=512M
> > 9) crashkernel=4G,high						//high=4G, low=256M
> > a) crashkernel=4G,high crashkernel=512M,low			//high=4G, low=512M
> > b) crashkernel=512M,high crashkernel=128M,low			//high=512M, low=128M
> > c) crashkernel=128M,high					//high=128M, low=256M
> > d) crashkernel=512M,low						//high=0G, low=0M, invalid
> > e) crashkernel=512M,high crashkernel=0,low			//high=512M, low=0M
> > f) crashkernel=4G,high crashkernel=ab,low			//high=0G, low=0M, invalid
> > 
> > 
> > Changes since [v19]:
> > 1. Temporarily stop making reserve_crashkernel[_low]() generic. There are a
> >    lot of details need to be considered, which can take a long time. Because
> >    "make generic" does not add new functions and does not improve performance,
> >    maybe I should say it's just a cleanup. So by stripping it out and leaving
> >    it for other patches later, we can aggregate the changes to the main functions.
> > 2. Use insert_resource() to replace request_resource(), this not only simplifies
> >    the code, but also reduces the differences between arm64 and x86 implementations.
> > 3. As commit 157752d84f5d ("kexec: use Crash kernel for Crash kernel low") do for
> >    x86, we can also extend kexec-tools for arm64, and it's currently applied. See:
> >    https://www.spinics.net/lists/kexec/msg28284.html
> > 
> > Thank you very much, Borislav Petkov, for so many valuable comments.
> > 
> > Changes since [v17]: v17 --> v19
> > 1. Patch 0001-0004
> >    Introduce generic parse_crashkernel_high_low() to bring the parsing of
> >    "crashkernel=X,high" and the parsing of "crashkernel=X,low" together,
> >    then use it instead of the call to parse_crashkernel_{high|low}(). Two
> >    confusing parameters of parse_crashkernel_{high|low}() are deleted.
> > 
> >    I previously sent these four patches separately:
> >    [1] https://lkml.org/lkml/2021/12/25/40
> > 2. Patch 0005-0009
> >    Introduce generic reserve_crashkernel_mem[_low](), the implementation of
> >    these two functions is based on function reserve_crashkernel[_low]() in
> >    arch/x86/kernel/setup.c. There is no functional change for x86.
> >    1) The check position of xen_pv_domain() does not change.
> >    2) Still 1M alignment for crash kernel fixed region, when 'base' is specified.
> > 
> >    To avoid compilation problems on other architectures: patch 0004 moves
> >    the definition of global variable crashk[_low]_res from kexec_core.c to
> >    crash_core.c, and provide default definitions for all macros involved, a
> >    particular platform can redefine these macros to override the default
> >    values.
> > 3. 0010, only one line of comment was changed.
> > 4. 0011
> >    1) crashk_low_res may also a valid reserved memory, should be checked
> >       in crash_is_nosave(), see arch/arm64/kernel/machine_kexec.
> >    2) Drop memblock_mark_nomap() for crashk_low_res, because of:
> >       2687275a5843 arm64: Force NO_BLOCK_MAPPINGS if crashkernel reservation is required
> >    3) Also call kmemleak_ignore_phys() for crashk_low_res, because of:
> >       85f58eb18898 arm64: kdump: Skip kmemleak scan reserved memory for kdump
> > 5. 0012, slightly rebased, because the following patch is applied in advance. 
> >    https://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git/commit/?h=dt/linus&id=8347b41748c3019157312fbe7f8a6792ae396eb7
> > 6. 0013, no change.
> > 
> > Others:
> > 1. Discard add ARCH_WANT_RESERVE_CRASH_KERNEL
> > 2. When allocating crash low memory, the start address still starts from 0.
> >    low_base = memblock_phys_alloc_range(low_size, CRASH_ALIGN, 0, CRASH_ADDR_LOW_MAX);
> > 3. Discard change (1ULL << 32) to CRASH_ADDR_LOW_MAX.
> > 4. Ensure the check position of xen_pv_domain() have no change.
> > 5. Except patch 0010 and 0012, all "Tested-by", "Reviewed-by", "Acked-by" are removed.
> > 6. Update description.
> > 
> > 
> > 
> > Changes since [v16]
> > - Because no functional changes in this version, so add
> >   "Tested-by: Dave Kleikamp <dave.kleikamp@oracle.com>" for patch 1-9
> > - Add "Reviewed-by: Rob Herring <robh@kernel.org>" for patch 8
> > - Update patch 9 based on the review comments of Rob Herring
> > - As Catalin Marinas's suggestion, merge the implementation of
> >   ARCH_WANT_RESERVE_CRASH_KERNEL into patch 5. Ensure that the
> >   contents of X86 and ARM64 do not overlap, and reduce unnecessary
> >   temporary differences.
> > 
> > Changes since [v15]
> > -  Aggregate the processing of "linux,usable-memory-range" into one function.
> >    Only patch 9-10 have been updated.
> > 
> > Changes since [v14]
> > - Recovering the requirement that the CrashKernel memory regions on X86
> >   only requires 1 MiB alignment.
> > - Combine patches 5 and 6 in v14 into one. The compilation warning fixed
> >   by patch 6 was introduced by patch 5 in v14.
> > - As with crashk_res, crashk_low_res is also processed by
> >   crash_exclude_mem_range() in patch 7.
> > - Due to commit b261dba2fdb2 ("arm64: kdump: Remove custom linux,usable-memory-range handling")
> >   has removed the architecture-specific code, extend the property "linux,usable-memory-range"
> >   in the platform-agnostic FDT core code. See patch 9.
> > - Discard the x86 description update in the document, because the description
> >   has been updated by commit b1f4c363666c ("Documentation: kdump: update kdump guide").
> > - Change "arm64" to "ARM64" in Doc.
> > 
> > 
> > Changes since [v13]
> > - Rebased on top of 5.11-rc5.
> > - Introduce config CONFIG_ARCH_WANT_RESERVE_CRASH_KERNEL.
> > Since reserve_crashkernel[_low]() implementations are quite similar on
> > other architectures, so have CONFIG_ARCH_WANT_RESERVE_CRASH_KERNEL in
> > arch/Kconfig and select this by X86 and ARM64.
> > - Some minor cleanup.
> > 
> > Changes since [v12]
> > - Rebased on top of 5.10-rc1.
> > - Keep CRASH_ALIGN as 16M suggested by Dave.
> > - Drop patch "kdump: add threshold for the required memory".
> > - Add Tested-by from John.
> > 
> > Changes since [v11]
> > - Rebased on top of 5.9-rc4.
> > - Make the function reserve_crashkernel() of x86 generic.
> > Suggested by Catalin, make the function reserve_crashkernel() of x86 generic
> > and arm64 use the generic version to reimplement crashkernel=X.
> > 
> > Changes since [v10]
> > - Reimplement crashkernel=X suggested by Catalin, Many thanks to Catalin.
> > 
> > Changes since [v9]
> > - Patch 1 add Acked-by from Dave.
> > - Update patch 5 according to Dave's comments.
> > - Update chosen schema.
> > 
> > Changes since [v8]
> > - Reuse DT property "linux,usable-memory-range".
> > Suggested by Rob, reuse DT property "linux,usable-memory-range" to pass the low
> > memory region.
> > - Fix kdump broken with ZONE_DMA reintroduced.
> > - Update chosen schema.
> > 
> > Changes since [v7]
> > - Move x86 CRASH_ALIGN to 2M
> > Suggested by Dave and do some test, move x86 CRASH_ALIGN to 2M.
> > - Update Documentation/devicetree/bindings/chosen.txt.
> > Add corresponding documentation to Documentation/devicetree/bindings/chosen.txt
> > suggested by Arnd.
> > - Add Tested-by from Jhon and pk.
> > 
> > Changes since [v6]
> > - Fix build errors reported by kbuild test robot.
> > 
> > Changes since [v5]
> > - Move reserve_crashkernel_low() into kernel/crash_core.c.
> > - Delete crashkernel=X,high.
> > - Modify crashkernel=X,low.
> > If crashkernel=X,low is specified simultaneously, reserve spcified size low
> > memory for crash kdump kernel devices firstly and then reserve memory above 4G.
> > In addition, rename crashk_low_res as "Crash kernel (low)" for arm64, and then
> > pass to crash dump kernel by DT property "linux,low-memory-range".
> > - Update Documentation/admin-guide/kdump/kdump.rst.
> > 
> > Changes since [v4]
> > - Reimplement memblock_cap_memory_ranges for multiple ranges by Mike.
> > 
> > Changes since [v3]
> > - Add memblock_cap_memory_ranges back for multiple ranges.
> > - Fix some compiling warnings.
> > 
> > Changes since [v2]
> > - Split patch "arm64: kdump: support reserving crashkernel above 4G" as
> > two. Put "move reserve_crashkernel_low() into kexec_core.c" in a separate
> > patch.
> > 
> > Changes since [v1]:
> > - Move common reserve_crashkernel_low() code into kernel/kexec_core.c.
> > - Remove memblock_cap_memory_ranges() i added in v1 and implement that
> > in fdt_enforce_memory_region().
> > There are at most two crash kernel regions, for two crash kernel regions
> > case, we cap the memory range [min(regs[*].start), max(regs[*].end)]
> > and then remove the memory range in the middle.
> > 
> > v1:
> > There are following issues in arm64 kdump:
> > 1. We use crashkernel=X to reserve crashkernel below 4G, which
> > will fail when there is no enough low memory.
> > 2. If reserving crashkernel above 4G, in this case, crash dump
> > kernel will boot failure because there is no low memory available
> > for allocation.
> > 
> > To solve these issues, change the behavior of crashkernel=X.
> > crashkernel=X tries low allocation in DMA zone and fall back to high
> > allocation if it fails.
> > 
> > We can also use "crashkernel=X,high" to select a high region above
> > DMA zone, which also tries to allocate at least 256M low memory in
> > DMA zone automatically and "crashkernel=Y,low" can be used to allocate
> > specified size low memory.
> > 
> > When reserving crashkernel in high memory, some low memory is reserved
> > for crash dump kernel devices. So there may be two regions reserved for
> > crash dump kernel.
> > In order to distinct from the high region and make no effect to the use
> > of existing kexec-tools, rename the low region as "Crash kernel (low)",
> > and pass the low region by reusing DT property
> > "linux,usable-memory-range". We made the low memory region as the last
> > range of "linux,usable-memory-range" to keep compatibility with existing
> > user-space and older kdump kernels.
> > 
> > Besides, we need to modify kexec-tools:
> > arm64: support more than one crash kernel regions(see [1])
> > 
> > Another update is document about DT property 'linux,usable-memory-range':
> > schemas: update 'linux,usable-memory-range' node schema(see [2])
> > 
> > 
> > [1]: https://www.spinics.net/lists/kexec/msg28226.html
> > [2]: https://github.com/robherring/dt-schema/pull/19 
> > [v1]: https://lkml.org/lkml/2019/4/2/1174
> > [v2]: https://lkml.org/lkml/2019/4/9/86
> > [v3]: https://lkml.org/lkml/2019/4/9/306
> > [v4]: https://lkml.org/lkml/2019/4/15/273
> > [v5]: https://lkml.org/lkml/2019/5/6/1360
> > [v6]: https://lkml.org/lkml/2019/8/30/142
> > [v7]: https://lkml.org/lkml/2019/12/23/411
> > [v8]: https://lkml.org/lkml/2020/5/21/213
> > [v9]: https://lkml.org/lkml/2020/6/28/73
> > [v10]: https://lkml.org/lkml/2020/7/2/1443
> > [v11]: https://lkml.org/lkml/2020/8/1/150
> > [v12]: https://lkml.org/lkml/2020/9/7/1037
> > [v13]: https://lkml.org/lkml/2020/10/31/34
> > [v14]: https://lkml.org/lkml/2021/1/30/53
> > [v15]: https://lkml.org/lkml/2021/10/19/1405
> > [v16]: https://lkml.org/lkml/2021/11/23/435
> > [v17]: https://lkml.org/lkml/2021/12/10/38
> > [v18]: https://lkml.org/lkml/2021/12/22/424
> > [v19]: https://lkml.org/lkml/2021/12/28/203
> > [v20]: https://lkml.org/lkml/2022/1/24/167
> > [v21]: https://lkml.org/lkml/2022/2/26/350
> > 
> > Chen Zhou (2):
> >   arm64: kdump: Reimplement crashkernel=X
> >   of: fdt: Add memory for devices by DT property
> >     "linux,usable-memory-range"
> > 
> > Zhen Lei (7):
> >   kdump: return -ENOENT if required cmdline option does not exist
> >   arm64: Use insert_resource() to simplify code
> >   arm64: kdump: Remove some redundant checks in map_mem()
> >   arm64: kdump: Don't force page-level mappings for memory above 4G
> >   arm64: kdump: Use page-level mapping for the high memory of
> >     crashkernel
> >   arm64: kdump: Try not to use NO_BLOCK_MAPPINGS for memory under 4G
> >   docs: kdump: Update the crashkernel description for arm64
> > 
> >  .../admin-guide/kernel-parameters.txt         |   8 +-
> >  arch/arm64/include/asm/kexec.h                |   2 +
> >  arch/arm64/kernel/machine_kexec.c             |   9 +-
> >  arch/arm64/kernel/machine_kexec_file.c        |  12 +-
> >  arch/arm64/kernel/setup.c                     |  17 +-
> >  arch/arm64/mm/init.c                          | 204 +++++++++++++++++-
> >  arch/arm64/mm/mmu.c                           |  68 +++---
> >  drivers/of/fdt.c                              |  33 ++-
> >  kernel/crash_core.c                           |   3 +-
> >  9 files changed, 278 insertions(+), 78 deletions(-)
> > 
> 
> -- 
> Regards,
>   Zhen Lei
>