linux-kernel - Re: [Xen-devel] [PATCH 2/4] xen/x86: Use memblock

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Date:	Mon, 30 Jul 2012 15:43:48 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Konrad Rzeszutek Wilk <konrad@...nok.org>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 2/4] xen/x86: Use memblock_reserve for
 sensitive areas.

On Fri, 27 Jul 2012, Konrad Rzeszutek Wilk wrote:
> On Fri, Jul 27, 2012 at 11:49:02AM +0100, Stefano Stabellini wrote:
> > On Thu, 26 Jul 2012, Konrad Rzeszutek Wilk wrote:
> > > instead of a big memblock_reserve. This way we can be more
> > > selective in freeing regions (and it also makes it easier
> > > to understand where is what).
> > > 
> > > [v1: Move the auto_translate_physmap to proper line]
> > > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > > ---
> > >  arch/x86/xen/enlighten.c |   38 ++++++++++++++++++++++++++++++++++++++
> > >  arch/x86/xen/p2m.c       |    5 +++++
> > >  arch/x86/xen/setup.c     |    9 ---------
> > >  3 files changed, 43 insertions(+), 9 deletions(-)
> > > 
> > > diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> > > index ff962d4..9b1afa4 100644
> > > --- a/arch/x86/xen/enlighten.c
> > > +++ b/arch/x86/xen/enlighten.c
> > > @@ -998,7 +998,44 @@ static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high)
> > >  
> > >  	return ret;
> > >  }
> > > +static void __init xen_reserve_mfn(unsigned long mfn)
> > > +{
> > > +	unsigned long pfn;
> > > +
> > > +	if (!mfn)
> > > +		return;
> > > +	pfn = mfn_to_pfn(mfn);
> > > +	if (phys_to_machine_mapping_valid(pfn))
> > > +		memblock_reserve(PFN_PHYS(pfn), PAGE_SIZE);
> > > +}
> > 
> > If the mfn is not in the m2p xen_reserve_mfn won't do anything. It is
> > worth writing it down in a comment.
> 
> Meaning in a printk?

I meant a comment in the code.


> > > +static void __init xen_reserve_internals(void)
> > > +{
> > > +	unsigned long size;
> > > +
> > > +	if (!xen_pv_domain())
> > > +		return;
> > > +
> > > +	memblock_reserve(__pa(xen_start_info), PAGE_SIZE);
> > 
> > xen_start_info is not in the m2p, so you cannot use xen_reserve_mfn
> 
> It seems to work for me. For both the toolstack created guests
> and dom0. Let me double check thought.

I was just thinking out loud: you are calling memblock_reserve rather
than xen_reserve_mfn, because xen_reserve_mfn wouldn't work in this case
as xen_start_info is not in the m2p.
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