linux-kernel - Re: [PATCH V2 1/2] RISC-V: Add arch_crash_save

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Message-ID: <Y02y9eN1TNJteTw6@spud>
Date:   Mon, 17 Oct 2022 20:54:29 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Xianting Tian <xianting.tian@...ux.alibaba.com>
Cc:     paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, anup@...infault.org, heiko@...ech.de,
        guoren@...nel.org, mick@....forth.gr,
        alexandre.ghiti@...onical.com, bhe@...hat.com, vgoyal@...hat.com,
        dyoung@...hat.com, corbet@....net, Conor.Dooley@...rochip.com,
        bagasdotme@...il.com, kexec@...ts.infradead.org,
        linux-doc@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, crash-utility@...hat.com,
        heinrich.schuchardt@...onical.com, k-hagio-ab@....com,
        hschauhan@...ltrace.org, yixun.lan@...il.com
Subject: Re: [PATCH V2 1/2] RISC-V: Add arch_crash_save_vmcoreinfo support

On Fri, Oct 14, 2022 at 09:41:38PM +0800, Xianting Tian wrote:
> Add arch_crash_save_vmcoreinfo(), which exports VM layout(MODULES, VMALLOC,
> VMEMMAP and KERNEL_LINK_ADDR ranges), va bits and ram base for vmcore.
> 
> Default pagetable levels and PAGE_OFFSET aren't same for different kernel
> version as below. For default pagetable levels, it sets sv57 on defaultly
> in latest kernel and do fallback to try to set sv48 on boot time if sv57
> is not supported in current hardware.

nit: This would read better as "it sets sv57 by default and falls back
to setting sv48 at boot time if sv57 is not supported by the hardware".

> 
> For ram base, the default value is 0x80200000 for qemu riscv64 env, 0x200000
> for riscv64 SoC platform(eg, SoC platform of RISC-V XuanTie 910 CPU).

The second part of this sentence I'm not really sure that that is true,
I think you should reword it to something like "...for qemu riscv64 and,
for example, is 0x200000 on the XuanTie 910 CPU." and avoid applying
that number blanketly for other SoCs.
> 
>  * Linux Kernel 5.18 ~
>  *      PGTABLE_LEVELS = 5
>  *      PAGE_OFFSET = 0xff60000000000000
>  * Linux Kernel 5.17 ~
>  *      PGTABLE_LEVELS = 4
>  *      PAGE_OFFSET = 0xffffaf8000000000
>  * Linux Kernel 4.19 ~
>  *      PGTABLE_LEVELS = 3
>  *      PAGE_OFFSET = 0xffffffe000000000
> 
> Since these configurations change from time to time and version to version,
> it is preferable to export them via vmcoreinfo than to change the crash's
> code frequently, it can simplify the development of crash tool.
> 
> Signed-off-by: Xianting Tian <xianting.tian@...ux.alibaba.com>
> ---
>  arch/riscv/kernel/Makefile     |  1 +
>  arch/riscv/kernel/crash_core.c | 29 +++++++++++++++++++++++++++++
>  2 files changed, 30 insertions(+)
>  create mode 100644 arch/riscv/kernel/crash_core.c
> 
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index db6e4b1294ba..4cf303a779ab 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -81,6 +81,7 @@ obj-$(CONFIG_KGDB)		+= kgdb.o
>  obj-$(CONFIG_KEXEC_CORE)	+= kexec_relocate.o crash_save_regs.o machine_kexec.o
>  obj-$(CONFIG_KEXEC_FILE)	+= elf_kexec.o machine_kexec_file.o
>  obj-$(CONFIG_CRASH_DUMP)	+= crash_dump.o
> +obj-$(CONFIG_CRASH_CORE)	+= crash_core.o
>  
>  obj-$(CONFIG_JUMP_LABEL)	+= jump_label.o
>  
> diff --git a/arch/riscv/kernel/crash_core.c b/arch/riscv/kernel/crash_core.c
> new file mode 100644
> index 000000000000..8d7f5ff108da
> --- /dev/null
> +++ b/arch/riscv/kernel/crash_core.c
> @@ -0,0 +1,29 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#include <linux/crash_core.h>
> +#include <linux/pagemap.h>
> +
> +void arch_crash_save_vmcoreinfo(void)
> +{
> +	VMCOREINFO_NUMBER(VA_BITS);
> +	VMCOREINFO_NUMBER(phys_ram_base);
> +
> +	vmcoreinfo_append_str("NUMBER(PAGE_OFFSET)=0x%lx\n", PAGE_OFFSET);
> +	vmcoreinfo_append_str("NUMBER(VMALLOC_START)=0x%lx\n", VMALLOC_START);
> +	vmcoreinfo_append_str("NUMBER(VMALLOC_END)=0x%lx\n", VMALLOC_END);
> +	vmcoreinfo_append_str("NUMBER(VMEMMAP_START)=0x%lx\n", VMEMMAP_START);
> +	vmcoreinfo_append_str("NUMBER(VMEMMAP_END)=0x%lx\n", VMEMMAP_END);
> +#ifdef CONFIG_64BIT
> +	vmcoreinfo_append_str("NUMBER(MODULES_VADDR)=0x%lx\n", MODULES_VADDR);
> +	vmcoreinfo_append_str("NUMBER(MODULES_END)=0x%lx\n", MODULES_END);
> +#endif
> +
> +	if (IS_ENABLED(CONFIG_64BIT)) {

You've already got a #ifdef CONFIG_64BIT above, is there a reason why
you'd use the IS_ENABLED here rather than merge this with the above
section? I'm a big fan of IS_ENABLED but I'm not sure what it adds here,
maybe you can show me the light :)

Thanks,
Conor.


> +#ifdef CONFIG_KASAN
> +		vmcoreinfo_append_str("NUMBER(KASAN_SHADOW_START)=0x%lx\n", KASAN_SHADOW_START);
> +		vmcoreinfo_append_str("NUMBER(KASAN_SHADOW_END)=0x%lx\n", KASAN_SHADOW_END);
> +#endif
> +		vmcoreinfo_append_str("NUMBER(KERNEL_LINK_ADDR)=0x%lx\n", KERNEL_LINK_ADDR);
> +		vmcoreinfo_append_str("NUMBER(ADDRESS_SPACE_END)=0x%lx\n", ADDRESS_SPACE_END);
> +	}
> +}
> -- 
> 2.17.1
> 
>