linux-kernel - Re: [PATCH v4 09/12] ppc64/kexec_file: setup backup region for kdump kernel

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Date:   Thu, 23 Jul 2020 21:28:55 -0300
From:   Thiago Jung Bauermann <bauerman@...ux.ibm.com>
To:     Hari Bathini <hbathini@...ux.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kernel test robot <lkp@...el.com>,
        Pingfan Liu <piliu@...hat.com>,
        Kexec-ml <kexec@...ts.infradead.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Petr Tesarik <ptesarik@...e.cz>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Sourabh Jain <sourabhjain@...ux.ibm.com>,
        lkml <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...abs.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Dave Young <dyoung@...hat.com>, Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH v4 09/12] ppc64/kexec_file: setup backup region for kdump kernel


Hari Bathini <hbathini@...ux.ibm.com> writes:

> Though kdump kernel boots from loaded address, the first 64K bytes
> of it is copied down to real 0. So, setup a backup region to copy
> the first 64K bytes of crashed kernel, in purgatory, before booting
> into kdump kernel. Also, update reserve map with backup region and
> crashed kernel's memory to avoid kdump kernel from accidentially
> using that memory.
>
> Reported-by: kernel test robot <lkp@...el.com>
> [lkp: In v1, purgatory() declaration was missing]
> Signed-off-by: Hari Bathini <hbathini@...ux.ibm.com>

Reviewed-by: Thiago Jung Bauermann <bauerman@...ux.ibm.com>

Just one minor comment below:

> @@ -1047,13 +1120,26 @@ int setup_new_fdt_ppc64(const struct kimage *image, void *fdt,
>  			goto out;
>  		}
>
> -		/* Ensure we don't touch crashed kernel's memory */
> -		ret = fdt_add_mem_rsv(fdt, 0, crashk_res.start);
> +		/*
> +		 * Ensure we don't touch crashed kernel's memory except the
> +		 * first 64K of RAM, which will be backed up.
> +		 */
> +		ret = fdt_add_mem_rsv(fdt, BACKUP_SRC_SIZE,

I know BACKUP_SRC_START is 0, but please forgive my pedantry when I say
that I think it's clearer if the start address above is changed to
BACKUP_SRC_START + BACKUP_SRC_SIZE...

> +				      crashk_res.start - BACKUP_SRC_SIZE);
>  		if (ret) {
>  			pr_err("Error reserving crash memory: %s\n",
>  			       fdt_strerror(ret));
>  			goto out;
>  		}
> +
> +		/* Ensure backup region is not used by kdump/capture kernel */
> +		ret = fdt_add_mem_rsv(fdt, image->arch.backup_start,
> +				      BACKUP_SRC_SIZE);
> +		if (ret) {
> +			pr_err("Error reserving memory for backup: %s\n",
> +			       fdt_strerror(ret));
> +			goto out;
> +		}
>  	}
>
>  out:

--
Thiago Jung Bauermann
IBM Linux Technology Center