linux-kernel - Re: [PATCH v6 8/8] x86/crash: Add x86 crash hotplug support for kexec

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Date:   Wed, 13 Apr 2022 21:13:59 +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, david@...hat.com,
        konrad.wilk@...cle.com, boris.ostrovsky@...cle.com
Subject: Re: [PATCH v6 8/8] x86/crash: Add x86 crash hotplug support for
 kexec_load

On 04/01/22 at 02:30pm, Eric DeVolder wrote:
> For kexec_file_load support, the loading of the crash kernel occurs
> entirely within the kernel, and as such the elfcorehdr is readily
> identified (so that it can be modified upon hotplug events).
> 
> This change enables support for kexec_load by identifying the
> elfcorehdr segment in the arch_crash_hotplug_handler(), if it has
> not already been identified.
> 
> Signed-off-by: Eric DeVolder <eric.devolder@...cle.com>

LGTM,

Acked-by: Baoquan He <bhe@...hat.com>

> ---
>  arch/x86/kernel/crash.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 101c030ac038..682f130b83e3 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -486,6 +486,30 @@ void arch_crash_hotplug_handler(struct kimage *image,
>  	void *elfbuf = NULL;
>  	unsigned long mem, memsz;
>  
> +	/*
> +	 * When the struct kimage is alloced, it is wiped to zero, so
> +	 * the elfcorehdr_index_valid defaults to false. It is set on the
> +	 * kexec_file_load path, or here for kexec_load, if not already
> +	 * identified.
> +	 */
> +	if (!image->elfcorehdr_index_valid) {
> +		unsigned int n;
> +
> +		for (n = 0; n < image->nr_segments; n++) {
> +			mem = image->segment[n].mem;
> +			memsz = image->segment[n].memsz;
> +			ptr = map_crash_pages(mem, memsz);
> +			if (ptr) {
> +				/* The segment containing elfcorehdr */
> +				if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
> +					image->elfcorehdr_index = (int)n;
> +					image->elfcorehdr_index_valid = true;
> +				}
> +			}
> +			unmap_crash_pages((void **)&ptr);
> +		}
> +	}
> +
>  	if (!image->elfcorehdr_index_valid) {
>  		pr_err("crash hp: unable to locate elfcorehdr segment");
>  		goto out;
> -- 
> 2.27.0
>