linux-kernel - Re: [RFC PATCH 00/13][V3] kexec: A new system call to allow in kernel loading

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Date:	Mon, 9 Jun 2014 09:57:05 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	ebiederm@...ssion.com, hpa@...or.com, mjg59@...f.ucam.org,
	greg@...ah.com, bp@...en8.de, jkosina@...e.cz, chaowang@...hat.com,
	bhe@...hat.com, akpm@...ux-foundation.org
Subject: Re: [RFC PATCH 00/13][V3] kexec: A new system call to allow in
 kernel loading

On 06/06/14 at 04:04pm, Vivek Goyal wrote:
> On Fri, Jun 06, 2014 at 03:37:48PM +0800, Dave Young wrote:
> > On 06/05/14 at 11:01am, Vivek Goyal wrote:
> > > On Thu, Jun 05, 2014 at 04:31:34PM +0800, Dave Young wrote:
> > > 
> > > [..]
> > > > > +	ret = kexec_file_load(kernel_fd, info.initrd_fd, info.command_line,
> > > > > +			info.command_line_len, info.kexec_flags);
> > > > 
> > > > Vivek,
> > > > 
> > > > I tried your patch on my uefi test machine, but kexec load fails like below:
> > > > 
> > > > [root@...alhost ~]# kexec -l /boot/vmlinuz-3.15.0-rc8+ --use-kexec2-syscall
> > > > Could not find a free area of memory of 0xa000 bytes ...
> > > 
> > > Hi Dave,
> > > 
> > > I think this message is coming from kexec-tools from old loading path. I
> > > think somehow new path did not even kick in. I tried above and I got
> > > -EBADF as I did not pass initrd. Can you run gdb on kexec and see if
> > > you are getting to syscall or run strace.
> > 
> > Seems I can not reproduce the local hole fail issue but I'm sure it happens
> > before the new syscall callback.
> > 
> > This time I got -ENOEXEC. It's caused by CONFIG_EFI_MIXED=y. In case EFI_MIXED
> > 64bit kernel runs on 32bit efi firmware thus XLF_CAN_BE_LOADED_ABOVE_4G is not
> > set thus bzImage probe will fail with NOEXEC.
> 
> Yep, current bzImage loader only supports loading 64bit image which can
> be loaded above 4G.
> 
> I am wondering how user space implementation is taking care of it. I guess
> we are falling back to 32bit implementation where we use 32bit entry and
> assume that bzImage has to be below 4G.
> 
> We will have to do similar thing in kernel when 32bit loader comes in.
> Compile that in for 64bit kernel and let it handle the case of bzImage
> not being loadable above 4G.

Vivek, I think current implementation is ok to only handle XLF_CAN_BE_LOADED_ABOVE_4G
bzImage.

Matt has sent a patch to revert the EFI_MIXED patch since 32bit loader never load
kernel to above 4G space. So no worry about this issue any more.

Thanks
Dave 
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