linux-kernel - Re: [PATCH 01/10] xen: Make all reserved pages for the balloon be INVALID_P2M

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Date:	Wed, 22 Dec 2010 09:53:27 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com,
	Jan Beulich <JBeulich@...ell.com>,
	xen-devel@...ts.xensource.com,
	Konrad Rzeszutek Wilk <konrad@...nel.org>
Subject: Re: [PATCH 01/10] xen: Make all reserved pages for the balloon be
 INVALID_P2M_ENTRY.

On Tue, Dec 21, 2010 at 02:19:40PM -0800, Jeremy Fitzhardinge wrote:
> On 12/21/2010 01:37 PM, Konrad Rzeszutek Wilk wrote:
> > This patch prepares ourselves for the case where void entries in the P2M
> > tree structure do not necessarily imply that the pages are missing.
> > With this, we diligently set regions that will be used by the
> > balloon driver to be INVALID_P2M_ENTRY and under the ownership
> > of the balloon driver.
> >
> > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> > ---
> >  arch/x86/xen/setup.c  |    8 ++++++++
> >  drivers/xen/balloon.c |    1 +
> >  2 files changed, 9 insertions(+), 0 deletions(-)
> >
> > diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> > index b5a7f92..d984d36 100644
> > --- a/arch/x86/xen/setup.c
> > +++ b/arch/x86/xen/setup.c
> > @@ -52,6 +52,8 @@ phys_addr_t xen_extra_mem_start, xen_extra_mem_size;
> >  
> >  static __init void xen_add_extra_mem(unsigned long pages)
> >  {
> > +	unsigned long pfn;
> > +
> >  	u64 size = (u64)pages * PAGE_SIZE;
> >  	u64 extra_start = xen_extra_mem_start + xen_extra_mem_size;
> >  
> > @@ -66,6 +68,11 @@ static __init void xen_add_extra_mem(unsigned long pages)
> >  	xen_extra_mem_size += size;
> >  
> >  	xen_max_p2m_pfn = PFN_DOWN(extra_start + size);
> > +
> > +	for (pfn = PFN_DOWN(extra_start); pfn <= xen_max_p2m_pfn; pfn++) {
> > +		BUG_ON(!set_phys_to_machine(pfn, INVALID_P2M_ENTRY));
> 
> Use __set_phys_to_machine where you don't expect (or can't allow) any
> allocation.

Are you OK with me moving then this check:

    if (unlikely(xen_feature(XENFEAT_auto_translated_physmap))) {
                BUG_ON(pfn != mfn && mfn != INVALID_P2M_ENTRY);
                return true;
        }    
from set_phys_to_machine to __set_phys_to_machine?

> 
> Also, I'm not a fan of hiding real side-effectful code in a BUG_ON
> predicate.

Ok. Will expunge these.
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