linux-kernel - Re: [PATCH] crash_dump: remove saved_max

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Message-ID: <87369py50x.fsf@x220.int.ebiederm.org>
Date:   Mon, 30 Mar 2020 15:14:06 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Kairui Song <kasong@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Young <dyoung@...hat.com>, kexec@...ts.infradead.org
Subject: Re: [PATCH] crash_dump: remove saved_max_pfn

Kairui Song <kasong@...hat.com> writes:

> This variable is no longer used.
>
> saved_max_pfn was originally introduce in commit 92aa63a5a1bf ("[PATCH]
> kdump: Retrieve saved max pfn"), used to make sure that user does not
> try to read the physical memory beyond saved_max_pfn. But since
> commit 921d58c0e699 ("vmcore: remove saved_max_pfn check")
> it's no longer used for the check.
>
> Only user left is Calary IOMMU, which start using it from
> commit 95b68dec0d52 ("calgary iommu: use the first kernels TCE tables
> in kdump"). But again, recently in commit 90dc392fc445 ("x86: Remove
> the calgary IOMMU driver"), Calary IOMMU is removed and this variable
> no longer have any user.
>
> So just remove it.
>
> Signed-off-by: Kairui Song <kasong@...hat.com>

Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>

Can we merge this through the tip tree?


> ---
>  arch/x86/kernel/e820.c     | 8 --------
>  include/linux/crash_dump.h | 2 --
>  kernel/crash_dump.c        | 6 ------
>  3 files changed, 16 deletions(-)
>
> diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
> index c5399e80c59c..4d13c57f370a 100644
> --- a/arch/x86/kernel/e820.c
> +++ b/arch/x86/kernel/e820.c
> @@ -910,14 +910,6 @@ static int __init parse_memmap_one(char *p)
>  		return -EINVAL;
>  
>  	if (!strncmp(p, "exactmap", 8)) {
> -#ifdef CONFIG_CRASH_DUMP
> -		/*
> -		 * If we are doing a crash dump, we still need to know
> -		 * the real memory size before the original memory map is
> -		 * reset.
> -		 */
> -		saved_max_pfn = e820__end_of_ram_pfn();
> -#endif
>  		e820_table->nr_entries = 0;
>  		userdef = 1;
>  		return 0;
> diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
> index 4664fc1871de..bc156285d097 100644
> --- a/include/linux/crash_dump.h
> +++ b/include/linux/crash_dump.h
> @@ -97,8 +97,6 @@ extern void unregister_oldmem_pfn_is_ram(void);
>  static inline bool is_kdump_kernel(void) { return 0; }
>  #endif /* CONFIG_CRASH_DUMP */
>  
> -extern unsigned long saved_max_pfn;
> -
>  /* Device Dump information to be filled by drivers */
>  struct vmcoredd_data {
>  	char dump_name[VMCOREDD_MAX_NAME_BYTES]; /* Unique name of the dump */
> diff --git a/kernel/crash_dump.c b/kernel/crash_dump.c
> index 9c23ae074b40..92da32275af5 100644
> --- a/kernel/crash_dump.c
> +++ b/kernel/crash_dump.c
> @@ -5,12 +5,6 @@
>  #include <linux/errno.h>
>  #include <linux/export.h>
>  
> -/*
> - * If we have booted due to a crash, max_pfn will be a very low value. We need
> - * to know the amount of memory that the previous kernel used.
> - */
> -unsigned long saved_max_pfn;
> -
>  /*
>   * stores the physical address of elf header of crash image
>   *