linux-kernel - Re: [Xen-devel] [PATCH v4] xen/grant-table: Avoid m2p

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Message-ID: <alpine.DEB.2.02.1401221848080.21510@kaball.uk.xensource.com>
Date:	Wed, 22 Jan 2014 18:50:20 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Zoltan Kiss <zoltan.kiss@...rix.com>
CC:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	<ian.campbell@...rix.com>, <wei.liu2@...rix.com>,
	<xen-devel@...ts.xenproject.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <jonathan.davies@...rix.com>
Subject: Re: [Xen-devel] [PATCH v4] xen/grant-table: Avoid m2p_override during
 mapping

On Wed, 22 Jan 2014, Zoltan Kiss wrote:
> On 22/01/14 16:39, Stefano Stabellini wrote:
> > On Tue, 21 Jan 2014, Zoltan Kiss wrote:
> > > @@ -121,7 +125,7 @@ static inline unsigned long mfn_to_pfn(unsigned long
> > > mfn)
> > >   		pfn = m2p_find_override_pfn(mfn, ~0);
> > >   	}
> > > 
> > > -	/*
> > > +	/*
> > 
> > Spurious change?
> It removes a stray space from the original code. Not necessary, but if it's
> there, I think we can keep it.

Usually cosmetic changes are done in a separate patch, or at the very
least they are mentioned in the commit message.


> > > diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> > > index 2ae8699..0060178 100644
> > > --- a/arch/x86/xen/p2m.c
> > > +++ b/arch/x86/xen/p2m.c
> > > @@ -872,15 +872,13 @@ static unsigned long mfn_hash(unsigned long mfn)
> > > 
> > >   /* Add an MFN override for a particular page */
> > >   int m2p_add_override(unsigned long mfn, struct page *page,
> > > -		struct gnttab_map_grant_ref *kmap_op)
> > > +		struct gnttab_map_grant_ref *kmap_op, unsigned long pfn)
> > 
> > Do we really need to add another additional parameter to
> > m2p_add_override?
> > I would just let m2p_add_override and m2p_remove_override call
> > page_to_pfn again. It is not that expensive.
> Yes, because that page_to_pfn can return something different. That's why the
> v2 patches failed.

I am really curious: how can page_to_pfn return something different?
I don't think is supposed to happen.
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