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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Message-Id: <50E70D8002000078000B336D@nat28.tlf.novell.com>
Date:	Fri, 04 Jan 2013 16:12:32 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Daniel Kiper" <daniel.kiper@...cle.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 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).

Jan

> 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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