Re: [PATCH v11 07/13] x86: add multiboot2 protocol support for EFI platforms

From: Daniel Kiper <daniel.kiper@oracle.com>
To: Doug Goldstein <cardoe@cardoe.com>
Cc: jgross@suse.com, sstabellini@kernel.org,
	andrew.cooper3@citrix.com, pgnet.dev@gmail.com,
	ning.sun@intel.com, julien.grall@arm.com, jbeulich@suse.com,
	xen-devel@lists.xenproject.org, qiaowei.ren@intel.com,
	gang.wei@intel.com, fu.wei@linaro.org
Subject: Re: [PATCH v11 07/13] x86: add multiboot2 protocol support for EFI platforms
Date: Fri, 13 Jan 2017 01:04:45 +0100	[thread overview]
Message-ID: <20170113000445.GB23864@olila.local.net-space.pl> (raw)
In-Reply-To: <ca20a3ca-56b5-fbed-3cfd-2fcf41707712@cardoe.com>

On Thu, Jan 12, 2017 at 04:23:59PM -0600, Doug Goldstein wrote:
> On 1/12/17 2:28 PM, Daniel Kiper wrote:
> > On Thu, Jan 12, 2017 at 09:52:15AM -0600, Doug Goldstein wrote:
> >> On 1/12/17 6:50 AM, Daniel Kiper wrote:
> >>> On Wed, Jan 11, 2017 at 02:20:15PM -0600, Doug Goldstein wrote:
> >>>> On 1/11/17 1:47 PM, Daniel Kiper wrote:
> >>>>> On Tue, Jan 10, 2017 at 02:51:27PM -0600, Doug Goldstein wrote:
> >>>>>> On 1/9/17 7:37 PM, Doug Goldstein wrote:

[...]

> >>>>>> memory region). You need to use AllocatePages() otherwise you are
> >>>>>> trampling memory that might have been allocated by the bootloader or any
> >>>>>
> >>>>> Bootloader code/data should be dead here.
> >>>>
> >>>> Correct. Unfortunately on my Lenovo laptop and my Intel NUCs I can't
> >>>> currently call ExitBootServices and a timer that iPXE has wired up has
> >>>
> >>> If you disable an important wheel in a machine you should not expect
> >>> that the machine will work. Sorry! No way!
> >>
> >> Speak to your co-workers Konrad and Boris. We've had long email threads
> >> about how certain hardware does not work with the way Xen calls
> >> ExitBootServices.
> >
> > Could you be more precise what is wrong? Or at least send links to
> > relevant threads.
>
> There have been several on the ML over the past 2 years. A quick Google
> search turns these up.
>
> http://xen.markmail.org/message/f6lx2ab4o2fch35r
> https://lists.xenproject.org/archives/html/xen-devel/2015-01/msg03164.html

This is more or less what I expected. However, IIRC, it was not related
to ExitBootServices() itself. The problem was that some runtime services
code lived in boot services code and data regions. So, I suppose that if
you map boot services code and data regions with runtime services code
and data everything should work. However, I have just realized that we
need an option to enable this functionality from GRUB2 command line.
Though you can do a test by setting map_bs to 1 at the beginning of
efi_multiboot2(). Do not forget to enable ExitBootServices() call in Xen.

> >>>> some memory reserved down there and it was getting trampled. The real
> >>>
> >>> I still do not know why remnants of iPXE should run at this Xen boot stage.
> >>> It looks like an iPXE bug and IMO it should be fixed first.
> >>
> >> Like I said above, its because on this machine I am unable to call Xen's
> >> EBS.
> >
> > I do not understand how ExitBootServices() call is related to iPXE timer remnants
> > or so. Though if it is related somehow then I think that you should blame machine
> > and/or iPXE designer/developer not Xen developer.
>
> iPXE registers a callback for when EBS is called to clean up a timer.

Could not you unregister this callback just before jump to the Xen image?
I do not think it is needed for Xen boot.

Daniel

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