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From: Vivek Goyal <vgoyal@redhat.com>
To: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Cc: lkml <linux-kernel@vger.kernel.org>,
	"linux-man@vger.kernel.org" <linux-man@vger.kernel.org>,
	kexec@lists.infradead.org, Andy Lutomirski <luto@amacapital.net>,
	Dave Young <dyoung@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Borislav Petkov <bp@alien8.de>,
	"Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: Edited kexec_load(2) [kexec_file_load()] man page for review
Date: Tue, 27 Jan 2015 09:24:59 -0500	[thread overview]
Message-ID: <20150127142459.GA12851@redhat.com> (raw)
In-Reply-To: <54B91271.3000600@gmail.com>

On Fri, Jan 16, 2015 at 02:30:25PM +0100, Michael Kerrisk (man-pages) wrote:
[..]
> 

Hi Michael,

Please find my responses below. Sorry, I got stuck in other work and
forgot about this thread.

> So, returning to the kexeec_segment structure:
> 
>            struct kexec_segment {
>                void   *buf;        /* Buffer in user space */
>                size_t  bufsz;      /* Buffer length in user space */
>                void   *mem;        /* Physical address of kernel */
>                size_t  memsz;      /* Physical address length */
>            };
> 
> Are the following statements correct:
> * buf + bufsz identify a memory region in the caller's virtual 
>   address space that is the source of the copy

Yes.

> * mem + memsz specify the target memory region of the copy

Yes.

> * mem is  physical memory address, as seen from kernel space

Yes.

> * the number of bytes copied from userspace is min(bufsz, memsz)

Yes. bufsz can not be more than memsz. There is a check to validate
this in kernel.

	result = -EINVAL;
	for (i = 0; i < nr_segments; i++) {
		if (image->segment[i].bufsz > image->segment[i].memsz)
			return result;
	}

> * if bufsz > memsz, then excess bytes in the user-space buffer 
>   are ignored.

You will get -EINVAL.

> * if memsz > bufsz, then excess bytes in the target kernel buffer
>   are filled with zeros.

Yes.

> Also, it seems to me that 'mem' need not be page aligned.
> Is that correct? Should the man page say something about that?
> (E.g., is it generally desirable that 'mem' should be page aligned?)

mem and memsz need to be page aligned. There is a check for that too.

	mstart = image->segment[i].mem;
	mend   = mstart + image->segment[i].memsz;
	if ((mstart & ~PAGE_MASK) || (mend & ~PAGE_MASK))
		return result;

> 
> Likewise, 'memsz' doesn't need to beta page multiple, IIUC.
> Should the man page say anything about this? For example, should 
> it note that the initialized kernel segment will be of size:
> 
>      (mem % PAGE_SIZE + memsz) rounded up to the next multiple of PAGE_SIZE
> 
> And should it note that if 'mem' is not a multiple of the page size, then
> the initial bytes (mem % PAGE_SIZE)) in the first page of the kernel segment 
> will be zeros?
> 
> (Hopefully I have read kimage_load_normal_segment() correctly.)

Both mem and memsz need to be page aligned.

> 
> And one further question. Other than the fact that they are used with 
> different system calls, what is the difference between KEXEC_ON_CRASH 
> and KEXEC_FILE_ON_CRASH?

Right now I can't think of any other difference. They both tell respective
system call that this kernel needs to be loaded in reserved memory region
for crash kernel.

Thanks
Vivek

  parent reply	other threads:[~2015-01-27 14:25 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-11-09 19:17 Michael Kerrisk (man-pages)
2014-11-11 21:30 ` Vivek Goyal
2015-01-07 21:17   ` Michael Kerrisk (man-pages)
2015-01-12 22:16     ` Vivek Goyal
2015-01-16 13:30       ` Michael Kerrisk (man-pages)
2015-01-27  8:07         ` Michael Kerrisk (man-pages)
2015-01-27 14:24         ` Vivek Goyal [this message]
2015-01-28  8:04           ` Michael Kerrisk (man-pages)
2015-01-28 14:48             ` Vivek Goyal
2015-01-28 15:49               ` Michael Kerrisk (man-pages)
2015-01-28 20:34                 ` Vivek Goyal
2015-01-28 21:14                   ` Scot Doyle
2015-01-28 21:31                     ` Vivek Goyal
2015-01-28 22:10                       ` Scot Doyle
2015-01-28 22:25                         ` Vivek Goyal
2015-01-29  1:27                           ` Scot Doyle
2015-01-29  5:39                             ` Michael Kerrisk (man-pages)
2015-01-29 16:06                               ` Scot Doyle
2015-01-30 15:25                                 ` Michael Kerrisk (man-pages)

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