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 18:25:38 +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 Fri, Jan 04, 2013 at 04:12:32PM +0000, Jan Beulich wrote:
> >>> On 04.01.13 at 16:15, Daniel Kiper <daniel.kiper@...cle.com> wrote:
> > 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);
> > ...
>
> I think that mapping is simply irrelevant, as the code at
> relocate_kernel gets copied to the control page and
> invoked there (other than in the native case, where
> relocate_kernel() gets invoked directly).

Right, so where is virtual mapping of control page established?
I could not find relevant code in SLES kernel which does that.

Daniel
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