linux-kernel - Re: [Xen-devel] Re: [Revert] Re: [PATCH] mm: sync vmalloc address space page tables in alloc_vm

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Date:	Fri, 2 Sep 2011 08:22:34 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"namhyung@...il.com" <namhyung@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	David Vrabel <david.vrabel@...rix.com>,
	"rientjes@...gle.com" <rientjes@...gle.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [Xen-devel] Re: [Revert] Re: [PATCH] mm: sync vmalloc address
 space page tables in alloc_vm_area()

On Thu, 2011-09-01 at 21:37 +0100, Jeremy Fitzhardinge wrote:
> On 09/01/2011 09:11 AM, Konrad Rzeszutek Wilk wrote:
> > On Thu, Sep 01, 2011 at 12:51:03PM +0100, David Vrabel wrote:
> >> From: David Vrabel <david.vrabel@...rix.com>
> > Andrew,
> >
> > I was wondering if you would be Ok with this patch for 3.1.
> >
> > It is a revert (I can prepare a proper revert if you would like
> > that instead of this patch).
> >
> > The users of this particular function (alloc_vm_area) are just
> > Xen. There are no others.
> 
> I'd prefer to put explicit vmalloc_sync_all()s in the callsites where
> necessary, and ultimately try to work out ways of avoiding it altogether
> (like have some hypercall wrapper which touches the arg memory to make
> sure its mapped?).

That only syncs the current pagetable though. If that is sufficient (and
it could well be) then perhaps just doing a vmalloc_sync_one on the
current page tables directly would be better than faulting to do it?

It's the sort of thing you could hide inside the gnttab_set_map_op type
helpers I guess?

Ian.


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