linux-kernel - Re: [PATCH 09/11] xen: introduce gnttab_map_refs and gnttab_unmap

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Date:	Mon, 10 Jan 2011 10:32:19 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Jeremy Fitzhardinge <Jeremy.Fitzhardinge@...rix.com>
Subject: Re: [PATCH 09/11] xen: introduce gnttab_map_refs and
 gnttab_unmap_refs

On Wed, 5 Jan 2011, Konrad Rzeszutek Wilk wrote:
> > +
> > +	ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, map_ops, count);
> > +
> > +	for (i = 0; i < count; i++) {
> > +		pfn = mfn_to_pfn(map_ops[i].host_addr >> PAGE_SHIFT);
> 
> Shouldn't you be checking the flag to see if this a bus address? You could
> also use the PFN_DOWN macro here..

Yes, actually I should be checking for GNTMAP_contains_pte.

> > +		pte = (pte_t *) __va((pfn << PAGE_SHIFT) +
> > +				(map_ops[i].host_addr & ~PAGE_MASK));
> 
> PFN_PHYS(pfn)? Or better You could use the mfn_to_virt macro here:
> 
> 		pte = (pte_t *) mfn_to_virt(PFN_DOWN(map_ops[i].ost_addr));
> 		pte += (map_ops[i].host_addr & _PAGE_MASK);
> 

Good suggestion, I have applied it (plus a small change to the pointer
arithmetic).

> > +		val = *pte;
> > +		mfn = (native_pte_val(val) & PTE_PFN_MASK) >> PAGE_SHIFT;
> 
> mfn = pte_mfn(pte) ?
> 

yep, done that.

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