linux-kernel - Re: [PATCH v3 02/11] x86/kexec: Add extra pointers to transition page table PGD, PUD, PMD and PTE

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Date:	Fri, 4 Jan 2013 16:15:42 +0100
From:	Daniel Kiper <daniel.kiper@...cle.com>
To:	Jan Beulich <JBeulich@...e.com>
Cc:	andrew.cooper3@...rix.com, x86@...nel.org, tglx@...utronix.de,
	kexec@...ts.infradead.org,
	virtualization@...ts.linux-foundation.org,
	xen-devel <xen-devel@...ts.xen.org>, konrad.wilk@...cle.com,
	maxim.uvarov@...cle.com, mingo@...hat.com, vgoyal@...hat.com,
	linux-kernel@...r.kernel.org, ebiederm@...ssion.com, hpa@...or.com
Subject: Re: [PATCH v3 02/11] x86/kexec: Add extra pointers to transition
 page table PGD, PUD, PMD and PTE

On Thu, Jan 03, 2013 at 09:34:55AM +0000, Jan Beulich wrote:
> >>> On 27.12.12 at 03:18, Daniel Kiper <daniel.kiper@...cle.com> wrote:
> > Some implementations (e.g. Xen PVOPS) could not use part of identity page table
> > to construct transition page table. It means that they require separate PUDs,
> > PMDs and PTEs for virtual and physical (identity) mapping. To satisfy that
> > requirement add extra pointer to PGD, PUD, PMD and PTE and align existing
> > code.
>
> So you keep posting this despite it having got pointed out on each
> earlier submission that this is unnecessary, proven by the fact that
> the non-pvops Xen kernels can get away without it. Why?

Sorry but I forgot to reply for your email last time.

I am still not convinced. I have tested SUSE kernel itself and it does not work.
Maybe I missed something but... Please check arch/x86/kernel/machine_kexec_64.c:init_transition_pgtable()

I can see:

vaddr = (unsigned long)relocate_kernel;

and later:

pgd += pgd_index(vaddr);
...

It is wrong. relocate_kernel() virtual address in Xen is different
than its virtual address in Linux Kernel. That is why transition
page table could not be established in Linux Kernel and so on...
How does this work in SUSE? I do not have an idea.

I am happy to fix that but whatever fix for it is
I would like to be sure that it works.

Daniel
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