linux-kernel - Re: [PATCH v4 05/10] crash hp: introduce helper functions un/map_crash

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Message-ID: <YhWwyTZuXxM4w+Fu@MiWiFi-R3L-srv>
Date:   Wed, 23 Feb 2022 11:58:01 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Eric DeVolder <eric.devolder@...cle.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.org, ebiederm@...ssion.com,
        dyoung@...hat.com, vgoyal@...hat.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, nramas@...ux.microsoft.com, thomas.lendacky@....com,
        robh@...nel.org, efault@....de, rppt@...nel.org,
        konrad.wilk@...cle.com, boris.ostrovsky@...cle.com
Subject: Re: [PATCH v4 05/10] crash hp: introduce helper functions
 un/map_crash_pages

On 02/09/22 at 02:57pm, Eric DeVolder wrote:
> This change introduces two new functions un/map_crash_pages()
> which are used to enable/disable access to the segments in the
> crash memory region. (Upon loading of a crash kernel, the
> crash memory regions are made inaccessible for integrity purposes.)
> 
> For example, on x86_64, one of the segments is the elfcorehdr,
> which contains the list of CPUs and memories. This segment
> needs to be modified in response to hotplug events. These functions
> are used to obtain (and subsequenntly release) access to the crash
> memory region in order to make the modifications.
> 
> QUESTION: These might need to be in arch/x86 as I'm not certain
> the implementatin is valid for all archs?

Since only x86_64 uses them, I would suggest putting them into x86_64,
near the caller.

> 
> Signed-off-by: Eric DeVolder <eric.devolder@...cle.com>
> ---
>  include/linux/kexec.h |  2 ++
>  kernel/crash_core.c   | 32 ++++++++++++++++++++++++++++++++
>  2 files changed, 34 insertions(+)
> 
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index b11d75a6b2bc..e00c373c4095 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -324,6 +324,8 @@ struct kimage {
>  };
>  
>  #ifdef CONFIG_CRASH_HOTPLUG
> +void *map_crash_pages(unsigned long paddr, unsigned long size);
> +void unmap_crash_pages(void **ptr);
>  void arch_crash_hotplug_handler(struct kimage *image,
>  	unsigned int hp_action, unsigned long a, unsigned long b);
>  #define KEXEC_CRASH_HP_REMOVE_CPU   0
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 256cf6db573c..0ff06d0698ad 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -9,6 +9,7 @@
>  #include <linux/init.h>
>  #include <linux/utsname.h>
>  #include <linux/vmalloc.h>
> +#include <linux/highmem.h>
>  
>  #include <asm/page.h>
>  #include <asm/sections.h>
> @@ -491,3 +492,34 @@ static int __init crash_save_vmcoreinfo_init(void)
>  }
>  
>  subsys_initcall(crash_save_vmcoreinfo_init);
> +
> +#ifdef CONFIG_CRASH_HOTPLUG
> +void *map_crash_pages(unsigned long paddr, unsigned long size)
> +{
> +	/*
> +	 * NOTE: The addresses and sizes passed to this routine have
> +	 * already been fully aligned on page boundaries. There is no
> +	 * need for massaging the address or size.
> +	 */
> +	void *ptr = NULL;
> +
> +	/* NOTE: requires arch_kexec_[un]protect_crashkres() for write access */
> +	if (size > 0) {
> +		struct page *page = pfn_to_page(paddr >> PAGE_SHIFT);
> +
> +		ptr = kmap(page);
> +	}
> +
> +	return ptr;
> +}
> +
> +void unmap_crash_pages(void **ptr)
> +{
> +	if (ptr) {
> +		if (*ptr)
> +			kunmap(*ptr);
> +		*ptr = NULL;
> +	}
> +}
> +#endif
> +
> -- 
> 2.27.0
>