linux-kernel - Re: [PATCH v19 2/7] crash: add generic infrastructure for crash hotplug support

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Message-ID: <ZBLrTl3UHYa1FV2S@MiWiFi-R3L-srv>
Date:   Thu, 16 Mar 2023 18:11:26 +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,
        sourabhjain@...ux.ibm.com, konrad.wilk@...cle.com,
        boris.ostrovsky@...cle.com
Subject: Re: [PATCH v19 2/7] crash: add generic infrastructure for crash
 hotplug support

On 03/06/23 at 11:22am, Eric DeVolder wrote:
......
> +static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
> +{
> +	/* Obtain lock while changing crash information */
> +	if (kexec_trylock()) {
> +
> +		/* Check kdump is loaded */
> +		if (kexec_crash_image) {
> +			struct kimage *image = kexec_crash_image;
> +
> +			if (hp_action == KEXEC_CRASH_HP_ADD_CPU ||
> +				hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
> +				pr_debug("hp_action %u, cpu %u\n", hp_action, cpu);
> +			else
> +				pr_debug("hp_action %u\n", hp_action);
> +
> +			/*
> +			 * When the struct kimage is allocated, the elfcorehdr_index
> +			 * is set to -1. Find the segment containing the elfcorehdr,
> +			 * if not already found. This works for both the kexec_load
> +			 * and kexec_file_load paths.
> +			 */
> +			if (image->elfcorehdr_index < 0) {
> +				unsigned long mem;
> +				unsigned char *ptr;
> +				unsigned int n;
> +
> +				for (n = 0; n < image->nr_segments; n++) {
> +					mem = image->segment[n].mem;
> +					ptr = kmap_local_page(pfn_to_page(mem >> PAGE_SHIFT));
> +					if (ptr) {
> +						/* The segment containing elfcorehdr */
> +						if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
> +							image->elfcorehdr_index = (int)n;
> +						}
> +						kunmap_local(ptr);
> +					}
> +				}
> +			}
> +
> +			if (image->elfcorehdr_index < 0) {
> +				pr_err("unable to locate elfcorehdr segment");
> +				goto out;
> +			}
> +
> +			/* Needed in order for the segments to be updated */
> +			arch_kexec_unprotect_crashkres();
> +
> +			/* Differentiate between normal load and hotplug update */
> +			image->hp_action = hp_action;
> +
> +			/* Now invoke arch-specific update handler */
> +			arch_crash_handle_hotplug_event(image);
> +
> +			/* No longer handling a hotplug event */
> +			image->hp_action = KEXEC_CRASH_HP_NONE;
> +			image->elfcorehdr_updated = true;

It's good to initialize the image->hp_action here, however where do
you check it? Do you plan to add some check somewhere?

> +
> +			/* Change back to read-only */
> +			arch_kexec_protect_crashkres();
> +		}
> +
> +out:
> +		/* Release lock now that update complete */
> +		kexec_unlock();
> +	}
> +}
......