linux-kernel - Re: [PATCH] /proc/kcore: Update physical address for kcore ram and text

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Date:   Wed, 25 Jan 2017 14:29:49 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Pratyush Anand <panand@...hat.com>
Cc:     linux-kernel@...r.kernel.org, bhe@...hat.com, anderson@...hat.com,
        kexec@...ts.infradead.org
Subject: Re: [PATCH] /proc/kcore: Update physical address for kcore ram and
 text

Hi Pratyush
On 01/25/17 at 10:14am, Pratyush Anand wrote:
> Currently all the p_paddr of PT_LOAD headers are assigned to 0, which is
> not true and could be misleading, since 0 is a valid physical address.

I do not know the history of /proc/kcore, so a question is why the
p_addr was set as 0, if there were some reasons and if this could cause
some risk or breakage.

> 
> User space tools like makedumpfile needs to know physical address for
> PT_LOAD segments of direct mapped regions. Therefore this patch updates
> paddr for such regions. It also sets an invalid paddr (-1) for other
> regions, so that user space tool can know whether a physical address
> provided in PT_LOAD is correct or not.
> 
> Signed-off-by: Pratyush Anand <panand@...hat.com>
> ---
>  fs/proc/kcore.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
> index 0b80ad87b4d6..ea9f3d1ae830 100644
> --- a/fs/proc/kcore.c
> +++ b/fs/proc/kcore.c
> @@ -373,7 +373,10 @@ static void elf_kcore_store_hdr(char *bufp, int nphdr, int dataoff)
>  		phdr->p_flags	= PF_R|PF_W|PF_X;
>  		phdr->p_offset	= kc_vaddr_to_offset(m->addr) + dataoff;
>  		phdr->p_vaddr	= (size_t)m->addr;
> -		phdr->p_paddr	= 0;
> +		if (m->type == KCORE_RAM || m->type == KCORE_TEXT)
> +			phdr->p_paddr	= __pa(m->addr);
> +		else
> +			phdr->p_paddr	= (elf_addr_t)-1;
>  		phdr->p_filesz	= phdr->p_memsz	= m->size;
>  		phdr->p_align	= PAGE_SIZE;
>  	}
> -- 
> 2.9.3
> 

Thanks
Dave